Process for oxidation of steroids and genetically engineered cells used therein

ABSTRACT

An expression cassette, operable in a recombinant host, comprising a heterologous DNA coding sequence encoding a protein, which is functional, alone or in cooperation with one or more additional proteins of catalyzing an oxidation step in the biological pathway, for conversion of cholesterol into hydrocortisone, which step is selected from the group consisting of: 
     the conversion of cholesterol to pregnenolone; 
     the conversion of pregnenolone to progesterone; 
     the conversion of progesterone to 17α-hydroxyprogesterone; 
     the conversion of 17α-hydroxyprogesterone to cortexolone; 
     the conversion of cortexolone to hydrocortisone, and the corresponding control sequences effective in that host.

PRIOR APPLICATIONS

This application is a division of U.S. application Ser. No. 08/418,085filed Apr. 6, 1995, now U.S. Pat. No. 5,869,283 which is acontinuation-in-part of U.S. patent application Ser. No. 08/054,185filed Apr. 26, 1993, now abandoned which is a continuation of U.S.patent application Ser. No. 07/474,857 filed Oct. 30, 1990, nowabandoned and U.S. patent application Ser. No. 08/002,608 filed Jan. 11,1993, now abandoned which is a continuation of U.S. patent applicationSer. No. 09/474,798 filed Jul. 16, 1990, now abandoned.

STATE OF THE ART

Δ⁴-pregneine-11β,17α,21-triol-3,20-dione (hydrocortisone) is animportant pharmaceutical steroid, used for its pharmacologicalproperties as a corticosteroid and as a starting compound for thepreparation of numerous useful steroids, particularly othercorticosteriods. Hydrocortisone is produced in the adrenal cortex ofvertebrates and was originally obtained, in small amounts only, by alaborious extraction from adrenal cortex tissue. Only after structureelucidation were new production routes developed, characterized by acombination of chemical synthesis steps and microbiological conversions.Only because the starting compounds which are employed such as sterols,bile acids and sapogenins are abundant and cheap, the present processesafford a less expensive product, but these still are rather complicated.Several possibilities were envisaged to improve the present processes,and also biochemical approaches have been tried.

One attempt was to have a suitable starting steroid converted in an invitro biochemical system using the isolated adrenal cortex proteinswhich are known to be responsible for the enzymatical conversion in vivoof steroids to hydrocortisone. However, the difficult isolation of theproteins and the high price of the necessary cofactors, appeared to beprohibitive for an economically attractive large scale process.

Another approach was to keep the catalyzing proteins in their naturalenvironment and to have the adrenal cortex cells produce the desiredhydrocortisone in a cell culture. But due to the low productivity of thecells, in practice, it appeared to be impossible to make such abiochemical process economically attractive.

The in vivo process in the adrenal cortex of mammals and othervertebrates constitutes a biochemical pathway, which starts withcholesterol and via various intermediate compounds eventually affordshydrocortisone (see FIG. 1). Eight proteins are directly involved inthis pathway, five of them being enzymes, among which four cytochromeP₄₅₀ enzymes, and the other three being electron transferring proteins.

The first step is the conversion of cholesterol to3β-hydroxy-5-pregnene-20-one (pregnenolone). In this conversion, amono-oxygenase reaction, three proteins are involved: side-chaincleaving enzyme (P₄₅₀SCC, a heme-Fe-containing protein), adrenodoxin(ADX, a Fe₂S₂ containing protein) and adrenodoxin reductase (ADR, aFAD-containing protein).

Besides cholesterol as a substrate, the reaction further requiresmolecular oxygen and NADPH. Subsequently, pregnenolone is converted bydehydrogenation/isomerization to Δ⁴-pregnene-3,20-dione (progesterone).This reaction, catalyzed by the protein 3β-hydroxy steroiddehydrogenase/isomerase (3β-HSD), requires pregnenolone, and NAD+.

To obtain hydrocortisone, progesterone subsequently is hydroxlated atthree positions which conversions are catalyzed by mono-oxygenases. Inthe conversions of progesterone into 17α-hydroxy progesterone, twoproteins are involved:

steroid 17α-hydroxylase (P₄₅₀17α, a heme-Fe-containing protein) andNADPH cytochrome P₄₅₀ reductase (RED, a FAD- and FMN-containingprotein). The reaction consumes progesterone, molecular oxygen andNADPH.

For the conversion of 17α-hydroxyprogesterone into17α,21-dihydroxy-Δ⁴-pregnene-3,20-dione (cortexolone), also two proteinsare needed: steroid-21-hydroxylase (P₄₅₀C21, a heme-Fe-containingprotein) and the before-mentioned protein RED. The reaction consumes17α-hydroxy progesterone, molecular oxygen and NADPH.

In the conversion of cortexolone into hydrocortisone, three proteins areinvolved: steroid 11β-hydroxylase (P₄₅₀11β, a heme-Fe-containingprotein), and the above mentioned proteins ADX and ADR.

As described above, cytochrome P₄₅₀ proteins are enzymes which areessential for the biochemical conversion of cholesterol tohydrocortisone. These enzymes belong to a larger group of cytochromeP₄₅₀ proteins (or shortly P₄₅₀ proteins). They have been encountered inprokaryotes (various bacteria) and eukaryotes (yeasts, molds, plants andanimals). In mammals, high levels of P₄₅₀ proteins are found in theadrenal cortex, ovary, testes and liver.

Many of these proteins, have been purified and are well characterizednow. Their specific activity has been determined. Recently, a number ofreviews on this subject have been published such as K. Ruckpaul and H.Rein (eds), “Cytochrome P₄₅₀” and P. R. Oritz de Montellano (ed.)“Cytochrome P₄₅₀, structure, mechanism and biochemistry”. CytochromeP₄₅₀ proteins are characterized by their specific absorbance maximum at450 nm after reduction with carbon monoxide. In prokaryotic organisms,the P₄₅₀ proteins are either membrane bound or cytoplasmatic. As far asthe bacterial, P₄₅₀ proteins have been studied in detail (e.g. P₄₅₀megand P₄₅₀cam), it has been shown that a ferredoxin and a ferredoxinreductase are involved in the hydroxylating activity. For eukaryoticorganisms, two types of P₄₅₀ proteins, I and II have been described.Their two differences reside in:

1. subcellular localization, type I is localized in the microsomalfraction and type II is localized in the inner membrane of mitochondria;

2. the way the electrons are transferred to the P₄₅₀ protein. Type I isreduced by NADPH via a P₄₅₀ reductase, whereas Type II is reduced byNADPH via a ferredoxin-reductase (e.g. adrenodoxin reductase) and aferredoxin (e.g. adrenodoxin).

According to EP-A-0,281,245, cytochrome P₄₅₀ enzymes can be preparedfrom Streptomyces species and used for the hydroxylation of chemicalcompounds. The enzymes are used in isolated form, which is a rathertedious and expensive procedure.

JP-A-62,236,485 (Derwent 87-331,234) teaches that it is possible tointroduce into Saccharomyces cerevisiae the genes of liver cytochromeP₄₅₀ enzymes and to express them affording enzymes which may be used fortheir oxidation activity. However, in the above references, there is noindication of the use of cytochrome P₄₅₀ enzymes for the preparation ofsteroid compounds.

OBJECTS OF THE INVENTION

It is an object of the invention to provide an improved biochemicalpathway for the production of hydrocortisone and expression cassettesuseful therein.

It is another object of the invention to provide recombinant host cellsand their progeny containing said expression cassettes.

These and other objects and advantages of the invention will becomeobvious from the following detailed description.

THE INVENTION

The process of the invention for the preparation of hydrocortisone fromsterols comprises culturing a recombinant cell in a nutrient medium, therecombinant host containing an expression cassette, operable in arecombinant host, comprising a heterologous DNA coding sequence encodinga protein, which is functional, alone or in cooperation with one or moreadditional proteins, of catalyzing an oxidation step in the biologicalpathway for conversion of cholesterol into hydrocortisone, which step isselected from the group consisting of:

the conversion of cholesterol to pregnenolone;

the conversion of pregnenolone to progesterone;

the conversion of progesterone to 17α-hydroxy-progesterone;

the conversion of 17α-hydroxyprogesterone to cortexolone;

the conversion of cortexolone to hydrocortisone, and the correspondingcontrol sequences effective in said host.

The invention provides a multiplicity of expression cassettes forproduction of proteins necessary in, the construction of a multigenicsystem for the one-step conversion of inexpensive steroid startingmaterials to more rare and expensive end products, wherein suchconversion is carried out in native systems through a multiplicity ofenzyme-catalyzed and cofactor-mediated conversions, such as theproduction of hydrocortisone from cholesterol. The expression cassettesof the invention are useful in the ultimate production of multigenicsystems for conducting these multi-step conversions.

Accordingly, in one aspect, the invention is directed to an expressioncassette effective in a recombinant host cell in expressing aheterologous coding DNA sequence, wherein said coding sequence encodesan enzyme which is able, alone or in cooperation with additionalproteins, to catalyze an oxidation step in the biological pathway forthe conversion of cholesterol to hydrocortisone. The expressioncassettes of the invention, therefore, include those sequences capableof producing, in a recombinant host, the following proteins: side-chaincleaving enzyme (P₄₅₀SCC); adrenodoxin (ADX); adrenodoxin reductase(ADR); 3β-hydroxy steroid dehydrogenase/isomerase (3β-HSD); steroid17α-hydrexylase (P₄₅₀17α); NADPH cytochrome P₄₅₀ reductase (RED);steroid-21-hydroxylase (P₄₅₀C21); and steroid 11β-hydroxylase (P₄₅₀11β).

In other aspects, the invention is directed to recombinant host cellstransformed with these vectors or with the expression cassettes off theinvention, to methods to produce the above enzymes and to use theseenzymes for oxidation, to processes to use said host cells for specificoxidations in a culture broth and to pharmaceutical compositionscontaining compounds prepared by said processes.

BRIEF DESCRIPTION OF THE FIGURES

Abbreviations used in all figures: R₁, EcoRI; H, HindIII; Sc, ScaI, P,PstI; K, KpnI; St, StuI; Sp, SphI; X, XbaI; N, NdeI; S, SmaI; Ss, SstI,R_(v), EcoRV; S_(I), SacI; B, BamHI; S_(II), SacII; Sal, SalI; Xh, XhoI;Pv, PvuII; Bg, BglII and M, MluI.

FIG. 1 shows a schematic overview of the proteins involved in thesucceeding steps in the conversion of cholesterol in hydrocortisone asoccurring in the adrenal cortex of mammals.

FIG. 2 shows the construction of plasmid pGBSCC-1. The P₄₅₀SCC-sequencesare indicated in a box ().

FIG. 3 shows the insertion of a synthetically derived PstI/HindIIIfragment (SEQ ID NO: 2) containing the 5′-P₄₅₀SCC-sequences into theplasmid pTZ18R to obtain the plasmid pTZ synlead.

FIG. 4 shows the construction of a full-length P₄₅₀SCC cDNA ofsynthetically () and by cDNA cloning () derived P₄₅₀SCC-sequences intopTZ18R to obtain pGBSCC-2.

FIG. 5 shows the complete nucleotide sequence of plasmid pBHA-1.

FIG. 6 is a schematic representation of the construction of pGBSCC-3.P₄₅₀SCC DNA sequences from plasmid pGBSCC-2 were introduced into theBacillus/E. coli shuttle plasmid pBHA-1 (SEQ ID NO: 3). Filled in boxesare as indicated in the legend of FIG. 4.

FIG. 7 shows the introduction of a NdeI restriction site (SEQ ID NO: 4)in combination with an ATG start codon before the P₄₅₀SCC-maturationsite (SEQ ID NO: 6) in pGBSCC-3 to obtain pGBSCC-4.

FIG. 8 shows a physical map of pGBSCC-5 which is obtained by removal ofE. coli sequences from the plasmid pGBSCC-4.

FIG. 9 shows a Western-blot probed with anti-bodies against P₄₅₀SCC,demonstrating the P₄₅₀SCC expression of plasmid pGBSCC-5 introduced inB. subtilis (lane c) and B. licheniformis (lane f). Control extracts,from B. subtilis (lane c) and B. licheniformis are shown in lanes (a)and (d) resp. For comparison also purified adrenal cortex P₄₅₀SCC (30ng) was added to these control extracts (lanes (b) and (e) resp.).

FIG. 10 is a schematic representation of the construction of pGBSCC-17.The coding P₄₅₀SCC-DNA sequences from plasmid pGBSCC-4 were introducedinto the E. coli expression vector pTZ18RN. The P₄₅₀SCC-sequences areindicated in a box ().

FIG. 11 shows the P₄₅₀SCC expression of pGBSCC-17 in E. coli JM101.

(a) SDS/PAGE and Coomassie brilliant blue staining of the cellularprotein fractions (20 μl) prepared from the E. coli control strain (lane3) and E. coli transformants SCC-301 and 302 (lanes 1 and 2, resp.). 400ng purified bovine P₄₅₀SCC (lane 4) is shown for comparison.

(b) Western-blot analysis probed with antibodies against P₄₅₀SCC ofcellular protein fractions (5 μl) prepared from the control strain E.coli JM101 (lane: 2) and from the E. coli JM101 (lane 3) and SCC-302(lane 4). 100 ng purified bovine P₄₅₀SCC (lane 1) is shown forcomparison.

FIG. 12 shows the construction of plasmid pUCG418.

FIG. 13 shows the construction of the yeast expression vector PGB950 byinsertion of the promoter and terminator with multiple cloning sites(SEQ ID NO: 8) () of lactase in pUCG418. To derive pGBSCC-6, a syntheticSalI/XhoI fragment (SEQ ID NO: 9) containing an ATG start codon and thecodons for the first 8 amino acids of P₄₅₀SCC is inserted in pGB950.

FIG. 14 is a schematic presentation showing the construction of theyeast P₄₅₀SCC-expression cassette pGBSCC-7.

FIG. 15 shows a Western-blot probed with antibodies specific for theprotein P₄₅₀SCC.

Blot A contains extracts derived from Saccharomyces cerevisiae 273-10Btransformed with pGBSCC-10 (lane 1); from S. cerevisiae 273-10B as acontrol (lane 2); from Kluyveromyces lactis CBS 2360 transformed withpGBSCC-7 (lane 3) and from K. lactis CBS 2360 as a control (lane 4).

Blot B contains extracts derived from K. lactis CBS 2360 as a control(lane 1) and K. lactis CBS 2360 transformed with pGBSCC-15 (lane 2),with pGBSCC-12 (lane 3) or with pGBSCC-7 (lane 4). Blot C containsextracts derived from S. cerevisiae 273-10B as a control (lane 1)transformed with pGBSCC-16 (lane 2) or with pGBSCC-13 (lane 3).

FIG. 16 is a schematic presentation of the construction of the yeastexpression vector pGBSCC-9 containing the isocytochrome CI (cyc-1).promoter from S. cerevisiae.

FIG. 17 shows a construction diagram of the P₄₅₀SCC cDNA containingexpression vector pGBSCC-10 for S. cerevisiae.

FIG. 18 shows the construction of the ₄₅₀SCC expression vector pGBSCC-12in which a synthetically derived DNA-fragment encoding the pre-P₄₅₀SCCsequence () is inserted 5′ for the coding sequence of mature P₄₅₀SCC.

FIG. 19 shows the construction of the pGBSCC-13. This P₄₅₀CCC expressioncassette for S. cerevisiae contains the pre-P₄₅₀SCC cDNA sequencepositioned 3′ of the cyc-1 promoter of S. cerevisiae.

FIG. 20 shows a schematic representation of the construction of theplasmids pGBSCC-14 and pGBSCC-15. The latter contains the P₄₅₀SCC codingsequence in frame with the cytochrome oxidase VI pre-sequence ().

FIG. 21 shows the construction of the plasmid pGBSCC-16. In thisplasmid, the cytochrome oxidase VI presequence () of S. cerevisiae fusedto the coding P₄₅₀SCC sequence is positioned 3′ of the cyc-1 promoter.

FIG. 22 shows the physical maps of the plasmids pGB17α-1 (A) andpGB17α-2 (B) containing the 3′ 1.4 kb fragment and the 5′ 345 bpfragment of P₄₅₀17α cDNA, resp. In pGB17α-3 (C) containing the fulllength P₄₅₀17α cDNA sequence, the position of the ATG start codon isindicated.

FIG. 23 shows the mutation of pGB17α-3 by in vitro mutagenesis (SEQ IDNO: 17). The obtained plasmid pGB17α-4 contains a SalI restriction site(SEQ ID NO: 18) followed by optimal yeast translation signals justupstream the ATG initiation codon.

FIG. 24 is a schematic view of the construction of the yeast P₄₅₀17αexpression cassette pGB17α-5.

FIG. 25 shows the mutation of pGB17α-3 by in vitro mutagenesis (SEQ IDNO: 19). The obtained plasmid pGB17α-6 contains an NdeI restriction site(SEQ ID NO: 20) at the ATG-initiation codon.

FIG. 26 is a schematic representation of the construction of pGB17α-7.P₄₅₀17α cDNA sequences from plasmid pGB17α-6 were introduced into theBacillus/E. coli shuttle plasmid pBHA-1.

FIG. 27 shows a physical map of pGB17α-8 which is obtained by removal ofE. coli sequences from the plasmid pGB17α-7.

FIG. 28 shows physical maps of pGBC21-1 and 2, containing an 1.53 kb3′-P₄₅₀C21 cDNA and a 540 bp 5′-P₄₅₀ cDNA EcoRI fragment, respectively,in the EcoRI-site of the cloning vector pTZ18R.

FIG. 29 shows the in vitro mutagenesis by the polymerase chain reaction(PCR) of pGBC21-2 (SEQ ID NOS: 26 and 27) to introduce EcoRV and NdeIrestriction sites (SEQ ID NO: 28 and 29) upstream the P₄₅₀C21ATG-initiation codon, followed by molecular cloning into the cloningvector pSP73 to derive pGBC21-3.

FIG. 30 is a schematic view of the construction of pGBC21-4, containingthe full-length P₄₅₀C21 cDNA sequence.

FIG. 31 is a schematic representation of the construction of pGBC21-5.The P₄₅₀C21 cDNA sequence from plasmid pGBC21-4 was introduced into theBacillus/E. coli shuttle plasmid pBHA-1.

FIG. 32 shows a physical map of pGBC21-6 which is obtained by removal ofE. coli sequences from the plasmid pGBC21-5.

FIG. 33 shows the mutation of pGBC21-2 by in vitro mutagenesis (SEQ IDNO: 31). The obtained plasmid pGBC21-7 contains a SalI restriction site(SEQ ID NO: 30) followed by optimal yeast translation signals justupstream the ATG initiation codon.

FIG. 34 represents the construction of pGBC21-8, containing afull-length P₄₅₀C21 cDNA with modified flanking restriction sitessuitable for cloning into the yeast expression vector.

FIG. 35 is a schematic presentation showing the construction of theyeast P₄₅₀C21-expression cassette pGBC21-9.

FIG. 36 shows the in vitro mutagenesis by the polymerase chain reactionof pGB11β-1 to introduce appropriate flanking restriction sites and anATG initiation codon to the full-length P₄₅₀11β cDNA sequence, followedby molecular cloning into the Bacillus/E. coli shuttle vector pBHA-1 toderive the plasmid pGB11β-2.

FIG. 37 shows the in vitro mutagenesis by the polymerase chain reactionof pGB11β-1 to introduce appropriate flanking restriction sites and anATG initiation codon to the full-length P₄₅₀11β cDNA sequence, followedby molecular cloning into the yeast expression vector pGB950 to derivethe plasmid PGB11β-4.

FIG. 38 is a schematic view of the molecular cloning of the ADX cDNAsequence from a bovine adrenal cortex polyA⁺RNA/cDNA mixture by thepolymerase chain reaction method. The cDNA sequence encoding the matureADX protein was inserted into the appropriate sites of the yeastexpression vector pGB950 to obtain the plasmid pGBADX-1.

FIG. 39 shows a Western-blot probed with antibodies against ADX,demonstrating the ADX expression of plasmid pGBADX-1 in K. lactis CBS2360 transformants ADX-101 and 102 (lanes 4 and 5, resp.). Extract ofcontrol strain K. lactis CBS 2360 is shown in lane 3. For comparison,also purified adrenal cortex ADX (100 ng) is supplied to the gel in lane1.

FIG. 40 shows the in vitro mutagenesis by the polymerase chain reactionof pGBADR-1 to introduce appropriate flanking restriction sites and anATG-initiation codon to the full-length ADR cDNA sequence, followed bymolecular cloning into the yeast expression vector pGB950 to derivepGBADR-2.

FIG. 41 shows a physical map of the expression cassette pGB17α-5.

FIG. 42 shows a physical map of the expression cassette pGBC21-9.

FIG. 43 represents the construction of the expression cassettepGB17α/C21-1, containing the coding sequence for P₄₅₀17α and P₄₅₀C21,both driven by the lactase promoter.

FIG. 44 shows a physical map of the plasmid pTG7457.

FIG. 45 shows a physical map of the plasmid pTG7453.

FIG. 46 shows a physical map of the plasmid pTG10014.

FIG. 47 shows a physical map of the plasmid pTG10004.

FIGS. 48 and 49, respectively show a physical map of the plasmidpTG10031 and pTG10033.

FIG. 50 shows a physical map of the plasmid pTG10013.

FIGS. 51 and 52, respectively show a physical map of the plasmidpTG10041 and pTG10042.

FIGS. 53 and 54, respectively show a physical map of the plasmidpTG10045 and pTG10046.

FIGS. 55 and 56, respectively show a physical map of the plasmidpTG10064 and pTG10065.

FIG. 57 is RP-HPLC analysis of Example 34.

The invention comprises the preparation and culturing of cells which aresuited to be used in large scale biochemical production reactors and theuse of these cells for the oxidation of compounds and particularly forthe production of steroids, shown in FIG. 1. Each of the depictedreactions can be carried out separately. Also interchange of steps in amulti-step reaction is included in the invention. Micro-organisms arepreferred hosts but other cells may be used as well as cells of plantsor animals, optionally applied in a cell culture or in the tissue ofliving transgenic plants or animals.

The cells of the invention are obtained by the genetic transformation ofsuitable receptor cells, preferably cells of suited micro-organisms,with vectors containing DNA sequences encoding the proteins involved inthe conversion of cholesterol to hydrocortisone, comprising side-chaincleaving, enzyme (P₄₅₀SCC), adrenodoxin (ADX), adrenodoxin reductase(ADR), 3β-hydroxy-steroid dehydrogenase/isomerase (3β-HSD)steroid-17α-hydroxylase (P₄₅₀17α), NADPH cytochrome P₄₅₀ reductase(RED), steroid-21-hydroxylase (P₄₅₀C21) and steroid-11β-hydroxylase(P₄₅₀11β). Some host cells may already produce on their own one or moreof the necessary proteins at a sufficient level and therefore have to betransformed with the supplementary DNA sequences only. Such possible ownproteins are ferredoxin, ferredoxin reductase, P₄₅₀-reductase, and3β-hydroxy-steroid dehydrogenase/isomerase.

For retrieval of the sequences which encode proteins which are involvedin the conversion of cholesterol to hydrocortisone, suitable DNA sourceshave been selected. An appropriate source for the retrieval of DNAencoding all proteins involved in the conversion of cholesterol tohydrocortisone is the adrenal cortex tissue of vertebrates e.g. bovineadrenal cortex tissue. Also from various micro-organisms, the relevantDNA can be retrieved, e.g. from Pseudomonas testosteroni, Streptomycesgriseocarneus or Brevibacterium sterolicum for DNA encoding the3β-hydroxy-steroid dehydrogenase/isomerase and from Curvularia lunata orCunninghamella blakesleeana for DNA encoding proteins involved in the11β-hydroxylation of cortexolone. The DNA-sequences coding for theproteins bovine P₄₅₀SCC, bovine P₄₅₀11β or a microbial equivalentprotein, bovine adrenodoxin, bovine adrenodoxin reductase,3β-hydroxy-steroid dehydrogenase/isomerase of bovine or microbialorigin, bovine P₄₅₀17α, bovine P₄₅₀C21 and NADPH cytochrome P₄₅₀reductase of bovine or microbial origin, were isolated according to thefollowing steps:

1. Eukaryotic Sequences (cDNA's)

a. Total RNA was prepared from appropriate tissue.

b. PolyA⁺ containing RNA was transcribed into double stranded cDNA andligated into bacteriophage vectors.

c. The obtained cDNA library was screened with ³²P-labeled oligomersspecific for the desired cDNA or by screening anisopropyl-β-D-thiogalactopyranoside (IPTG)-induced lambda-gt11 cDNAlibrary using a specific (¹²⁵I-labeled) antibody.

d. cDNA inserts of positive plaque forming units (pfu's) were insertedinto appropriate vectors to verify:

the entire length of the cDNA by nucleotide sequencing.

2. Prokaryotic Genes

a. Genomic DNA was prepared from an appropriate micro-organism.

b. To obtain a DNA library, DNA fragments were cloned into appropriatevectors and transformed to an appropriate E. coli host.

c. The DNA library was screened with ³²P-labeled oligomers specific forthe gene of interest or by screening an IPTG-induced lambda-gt11 cDNAlibrary using a specific (¹²⁵I-labeled) antibody.

d. Plasmids of positive colonies were isolated and inserted DNAfragments subcloned into appropriate vectors to verify:

the entire length of the gene.

Note: According to an improved method, the particular cDNA (eukaryoticsequences) or gene (prokaryotic sequences) was amplified using twospecific oligomers by the method known as the polymerase chain reaction(PCR) (Saiki et, al, Science, Vol. 239, pp. 487-491, 1988).Subsequently, the amplified cDNA or DNA was inserted into theappropriate vectors.

According to one aspect of the invention, suitable expression cassettesare provided in which the heterologous DNA isolated by the previousprocedure is placed between suitable control sequences for transcriptionand translation, which enables the DNA to be expressed in the cellularenvironment of a suitable host, affording the desired protein orproteins. Optionally, the initiation control sequences are followed by asecretion signal sequence.

Suitable control sequences have to be introduced together with thestructural DNA by said expression cassettes. Expression is made possibleby transformation of a suitable host cell with a vector containingcontrol sequences which are compatible with the relevant host and are inoperable linkage to the coding sequences of which expression is desired.

Alternatively, suitable control sequences present in the host genome areemployed. Expression is made possible by transformation of a suitablehost cell with a vector containing coding sequences of the desiredprotein flanked by host sequences enabling homologous recombination withthe host genome in such a manner that host control sequences properlycontrol the expression of the introduced DNA.

As is generally understood, the term control sequences comprises all DNAsegments which are necessary for the proper regulation of the expressionof the coding sequence to which they are operably linked, such asoperators, enhancers and, particularly, promoters and sequences whichcontrol the translation.

The promoter may or may not be controllable by regulating itsenvironment. Suitable promoters for prokaryotes include, for example,the trp promoter (inducible by tryptophan deprivation), the lac promoter(inducible with the galactose analog IPTG), the β-lactamase promoter,and the phage derived P_(L) promoter (inducible by temperaturevariation). Additionally, especially for expression in Bacillus, usefulpromoters include those for alpha-amylase, protease, Spo2, spac and ø105and synthetic promoter sequences. A preferred promoter is the onedepicted in FIG. 5 and denoted with “HpaII”.

Suitable promoters for expression in yeast include the3-phospho-glycerate kinase promoter and those for other glycolyticenzymes, as well as promoters for alcohol dehydrogenase and yeastphosphatase. Also suited are the promoters for transcription elongationfactor (TEF) and lactase. Mammalian expression systems generally employpromoters and the SV40 promoter but they also include regulatablepromoters such as the metallothionein promoter, which is controlled byheavy metals or gluco-corticoid concentration. Presently, viral-basedinsect cell expression systems are also suited, as well as expressionsystems based on plant cell promoters such as the nopaline synthetasepromoters.

Translation control sequences include a ribosome binding site (RBS) inprokaryotic systems, whereas in eukaryotic systems translation may becontrolled by a nucleotide sequence containing an initiation codon suchas AUG.

In addition to the necessary promoter and the translation controlsequence, a variety of other control sequences, including thoseregulating termination (for example, resulting in polyadenylationsequences in eukaryotic systems) may be used in controlling expression.Some systems contain enhancer elements which are desirable, but mostlynot obligatory, in effecting expression.

The invention also discloses expression cassettes containing stillanother heterologous coding sequence encoding an enzyme which catalyzes,alone or in cooperation with one or more additional proteins, anotherstep of the pathway of FIG. 1.

A group of vectors denoted with pGBSCC-n, where “n” is any integer from1 to 17, is especially developed for the DNA encoding the P₄₅₀SCCenzyme.

Another group of vectors denoted with pGB17α-n, where “n” is any integerfrom 1 to 5, is especially developed for the DNA encoding the P₄₅₀17αenzmye.

A further group of vectors denoted with pGBC21-n, where “n” is anyinteger from 1 to 9, is especially developed for the DNA encoding theP₄₅₀C21 enzyme.

Still another group of vectors denoted with pGB11β-n, where “n” is anyinteger from 1 to 4, is especially developed for the DNA encoding theP₄₅₀11β enzyme.

According to a further aspect of the invention, suitable host cells havebeen selected which accept the vectors of the invention and allow theintroduced DNA to be expressed. When culturing the transformed hostcells, the proteins involved in the conversion of cholesterol tohydro-cortisone appear in the cell contents. The presence of the desiredDNA can be proven by DNA hybridizing procedures, their transcription byRNA hybridization, their expression by immunological assays and theiractivity by assessing presence of oxidized products after incubationwith the starting compound in vitro or in vivo.

Transformed microorganisms are preferred hosts, particularly bacteria(more preferably Escherichia coli and Bacillus and Streptomyces species)and yeasts (such as Saccharomyces and Kluyveromyces). Other suitablehost organisms are found among plants and animals comprising insects, ofwhich the isolated cells are used in a cell culture, such as COS cells,C₁₂₇ cells, CHO cells, and Spodoptera frugiperda (Sf9) cells.Alternatively, a transgenic plant or animal is used.

A particular type of recombinant host cells are the ones, in whicheither two or more expression cassettes of the invention have beenintroduced or which have been transformed by an expression cassettecoding for at least two heterologous proteins, enabling the cell toproduce at least two proteins involved in the pathway of FIG. 1.

A major feature of the invention is that the prepared novel cells arenot only able to produce the proteins involved in the oxidativeconversion of steroids resulting eventually into hydrocortisone, butalso to use these proteins on the spot in the desired oxidativeconversion of the corresponding substrate compound added to the cultureliquid. Steroids are preferred substrates. The cells transformed withthee heterologous DNA are especially suited to be cultured with thesteroids mentioned in FIG. 1, including other sterols such asβ-sitosterol. As a result, oxidized steroids are obtained.

Depending oh the presence in the host cell of a multiplicity ofheterologous DNA encoding proteins involved in the pathway of FIG. 1,several biochemical conversions result comprising the a side-chaincleaving of a sterol and/or oxidative modifications of C11, C17, C3 andC21. Therefore, the expression cassettes of the invention are useful inconstructing a multigenic system which can effect successiveintra-cellular transformations of the multiple steps in the sequence asdepicted in FIG. 1. It may be necessary to introduce into the desiredhost expression cassettes which encode in their entirety the requiredproteins. In some instances, one or more of the proteins involved in thepathway may already be present in the host as a natural protein exertingthe same activity. For example, ferredoxin, ferredoxin reductase andP₄₅₀ reductase may already be present in the host. Under thosecircumstances, only the remaining enzymes must be provided byrecombinant transformation.

As an alternative to biochemical conversions in vivo, the proteinsinvolved in the conversion of cholesterol to hydrocortisone arecollected, purified as far as necessary, and used for the in vitroconversion of steroids in a cell free system, e.g. immobilized on acolumn. Alternatively, the more or less purified mixture containing oneor more enzymes of the pathway is used as such for steroid conversion.One exemplified host contains DNA encoding two heterologous proteinsviz. the enzyme P₄₅₀SCC and the protein ADX necessary for the productionof pregnenolone. In comparison with a host with only P₄₅₀SCC DNA, theyield of pregnenolone in a cell-free extract after adding ADR, NADPH andcholesterol is considerably improved.

The present invention provides expression cassettes necessary for theconstruction of a one-step production process for several usefulsteroids. Starting from cheap and abundantly available startingcompounds, it is especially suited from the production of hydrocortisoneand intermediate compounds. The invention renders obsolete traditionalexpensive chemical reactions. Intermediate compounds need not beisolated. Apart from the novel host cells, the processes used forculturing these cells on behalf of steroid conversions are analogous tobio-technological procedures well known in the art.

It has now been accomplished to clone in one host organism, the geneswhich code for the proteins which are able to catalyze two separateoxidations on the steroid molecule and particularly for the proteinsshown in FIG. 1. In particular, it has been realized to clone theproteins responsible for the steroid 17α-hydroxylation and for thesteroid C21-hydroxylation in one and the same host organism and to havesaid host organism express said proteins in a functional form. Moreover,in another aspect of the invention, a process is provided in which saidtransformed micro-organisms when grown in a fermentation medium oxidizea steroid substrate present in the medium simultaneously at twodifferent positions of the steroid molecule. In particular, a one-stepprocess is achieved for the introduction of the 17α- as well as the21-hydroxyl group.

A preferred host organism is Kluyveromyces lactis or is Saccharomycescerevisiae, but other host organisms and in particular micro-organisms,especially those previously mentioned, can be used. More particularly,the micro-organisms are suitable which have been described above forcloning and expressing the genes of the biochemical pathway as shown inFIG. 1.

One way to prepare a host able to carry out a multiple steroid oxidationis to transform the host with two or more vectors each containing thegene for one oxidation step. One exemplified transformed host containsDNA encoding the P₄₅₀17α and 3β-HSDH proteins. Another way is to havethe host transformed by one vector containing an expression cassettewith all genes coding for the proteins necessary for the desiredmultiple oxidation reaction. According to the invention, the expressioncassette contains at least two structural genes, each flanked by propercontrol sequences. One exemplified expression cassette contains DNAencoding the proteins P₄₅₀17α and P₄₅₀-C21 (pGB17-α/C21-1).

Using the method of the invention it is possible, using methods known inthe art, to prepare analogous expression cassettes and host cellscontaining them, with which it is possible to carry out other multiplesteroid oxidations and eventually the conversion of cholesterol intohydrocortisone in a single fermentation process.

In another embodiment of the invention, the 3β-hydroxy-5-ene steroiddehydrogenase and 5-ene-4-ene steroid isomerase (3β HSDH) form abifunctional enzyme which catalyzes two independant reactionstransforming pregenenolone into progesterone. The protein of 42 kD isencoded by a single open reading frame. cDNA's and/or genes have beencloned from human (Lachance et al., J. Biol. Chem. 265 (1990) p20469-20475 ; Lachance et al., DNA Cell Biol. 10 (1991) p 701-711),bovine (Zhao et al., FEBS lett. 259 (1989) p 153-157 and rat (Zhao etal., J. Biol. Chem. 266 (1990) p 583-593); Simard J. et al., J. Biol.Chem. 266 (1991) p 14842-14845). The determined N-terminus correspondsto the deduced amino acid sequence. In human, two types have beendescribed: type I 3β HSDH has been isolated from placenta and is alsoexpressed in skin; type II 3β HSDH was isolated from adrenals andgonads. Nucleotide homologies between exons 1 till 4 are 77.1, 91.8, 94and 94% respectively and 94% at the amino acid level. After expressionin HeLa cells of the respective cDNA's, it was found that the type Ienzyme is more active (Vmax/Km) on pregenenolone, DHEA(dehydroepiandrosterone) and DHT (dihydrotestosterone). This isprimarily due to a lower Km, e.g. for pregnenolone (0.24 versus 1.2 μM).Even in the absence of a mitochondrial targetting sequence, the 3β HSDHenzymes are known as membrane-associated proteins, located in microsomalas well as in mitochondrial membranes.

In the following examples, there are described several preferredembodiments to illustrate the invention. However, it should beunderstood that the invention is not intended to be limited to thespecific embodiments.

EXAMPLE 1 Molecular Cloning of a Full-length cDNA Encoding the BovineCytochrome P₄₅₀ Side Chain Cleavage Enzyme (P₄₅₀SCC)

General cloning techniques as well as DNA and RNA analyses have beenused as described in the handbook of T. Maniatis et al., MolecularCloning, Cold Spring Harbor Laboratory, 1982. Unless describedelsewhere, all DNA modifying enzymes, molecular cloning vehicles and E.coli strains were obtained from commercial suppliers and used accordingto the manufacturer's instructions. Materials and apparatus for DNA andRNA separation and purification were used according to instructions ofthe suppliers.

Bovine adrenal scortex tissue was prepared from freshly obtained bovinekidneys, quickly frozen in liquid nitrogen and stored at −80° C. Fromfrozen bovine adrenal cortex, total cellular RNA was prepared asdescribed by Auffrey et al (Eur. J. Biochem., Vol. 107, p. 303-314,1980). Adrenal poly A+ RNA was obtained by heating the total RNA sampleat 65° C. before polyA selection on oligo(dT) chromatography.

DNA's complementary to polyA⁺ RNA from bovine adrenal cortex weresynthesized as follows: 10 μg of polyA⁺ RNA, treated with methylmercurichydroxide were neutralized with β-mercaptoethanol and the mixture wasadjusted to 50 mM Tris/HCl (pH 8.3 at 42° C.), 40 mM KCl, 6 mM MgCl₂, 10mM DTT, 3000 U RNasin/ml, 4 mM Na₄P₂O₇, 50 μg actinomycine D/ml, 0.1 mgoligo(dT₁₂₋₁₈)/ml, 0.5 mM dGTP, 0.5 mM dATP, 0.5 mM dTTP, 0.25 mM dCTPand 400 μCi α ³²P-dCTP/ml, all in a final volume of 100 μl. The mixturewas put on ice for 10 minutes, heated for 2 minutes at 42° C. and thesynthesis was started by addition of 150 U AMV reverse transcriptase(Anglian Biotechnology Ltd.); incubation was performed for 1 hour at 42°C.

Second strand synthesis was performed by adding DNA polymerase and RNaseH according to Gubler et al (Gene, Vol. 25, pp. 263-269, 1983). Aftertreatment of the ds DNA with T4 DNA polymerase (BRL) to obtain bluntends, decameric EcoRI linkers (Biolabs Inc.) were ligated to the ds DNAfragments. After digestion with EcoRI-linkers by Biogel A15 m (Bio-Rad)chromatography. Approximately 200 ng EcoRI-linker containing doublestranded cDNA was ligated with 10 μg of EcoRI digested and calfintestine-phosphatase (Boehringer) treated with lambdagt11 vector DNA(Promega) by T4-DNA ligase (Boehringer) as described by Huynh et al.(In: “DNA cloning techniques: A practical approach”, pp. 49-78, OxfordIRL-press, 1985). Phages obtained after in vitro packaging of theligation mixture were used to infect the E. coli Y1090 host (Promega).

From this cDNA library, approximately 10⁶ plaque forming units (pfu's)were screened with a ³²P-end labeled synthetic oligomer SCC-1 (5′-GGCTGA CGA AGT CCT GAG ACA CTG GAT TCA GCA CTGG-3′), (SEQ ID NO: 1)specific for bovine P₄₅₀SCC DNA sequences as described by Morohashi etal. (Proc. Natl. Acad. Sci. USA, Vol. 81, pp. 4647-4651, 1984). Sixhybridizing pfu's were obtained and further purified by two additionalrounds of infection, plating and hybridization. The P₄₅₀SCCcDNA EcoRIinserts were subcloned into the EcoRI site of pTZ18R (Pharmacia). ClonepGBSCC-1 (FIG. 2), containing the largest EcoRI insert (1.4 kb), derivedfrom the clone lambdagt11 SCC-54 was further analyzed by restrictionenzyme mapping and sequencing.

The sequence data revealed that the pGBSCC-1 EcoRI insert was identicalwith the nucleotide sequence of SCCcDNA between positions 251 and 1824on the P₄₅₀SCCcDNA map as described by Morohashi et al.

The remaining 5′-P₄₅₀SCCcDNA nucleoptides were synthetically derived bycloning a 177 bp Pst/HindIII fragment (SEQ ID NO: 2) into theappropriate sites of pTZ18R, resulting in the pTZ/syn lead as shown inFIG. 3, containing besides the nucleotides coding for the mature P₄₅₀SCCprotein from position 188 to 273 as published by Morohashi et al.,additional restrictive sites for ScaI, AvrII and StuI without affectingthe predicted amino acid sequence of the P₄₅₀SCC protein.

The full-length P₄₅₀SCCcDNA was constructed by molecular cloning in E.coli JM101 (ATCC 33876) of a ligation mixture containing the 1372 bpHindIII/KpnI pGBSCC-1 fragment, the 177 bp Pst/HindIII pTZ/syn leadfragment and pTZ19R DNA digested with Psti and KpnI. The resultingplasmid, pGBSCC-2, containing all nucleotide sequences encoding themature bovine P₄₅₀ side chain cleavage protein is shown in FIG. 4.

EXAMPLE 2 Construction, Transformation and Expression of P₄₅₀SCC in theBacterial Host Bacillus subtilis

To derive expression of cytochrome P₄₅₀SCC in a Bacillus host,P₄₅₀SCCcDNA sequences were transferred to an E. coli/Bacillus shuttlevector pBHA-1.

FIG. 5 shows the nucleotide sequence of the shuttle plasmid pBHA-1 (SEQID NO: 3). The plasmid consists of positions 11-105 and 121-215:bacteriophage FD terminator (double); positions 221-307: a part ofplasmid pBR322 (viz. positions 2069-2153); positions 313-768:bacteriophage F1, origin of replication (viz. positions 5482-5943)positions 772-2571: part of plasmid pBR322, viz. the origin ofreplication and the β-lactamase gene; positions 2572-2685: transposonTN903, complete genome; positions 2719-2772: tryptophan terminator(double); positions 2773-3729: transposon Tn9, the chloramphenicolacetyltransferase gene. The nucleotides at position 3005 (A), 3038 (C), 3302(A) and 3409 (A) differed from the wild type cat coding sequence. Thesemutations were introduced to eliminate the NcoI, BalI, EcoRI and PvuIIsites: positions 3730-3804: multiple cloning site; positions 3807-7264:part of plasmid pUB110 containing the Bacillus “HpaII” promoter, thereplication function and kanamycin resistance gene (EcoRI-PvuIIfragment) (McKenzie et al., Plasmid, Vol. 15, pp 93-103, 1986 andMcKenzie et al., Plasmid, Vol. 17, pp. 83-85, 1987); positions7267-7331: multiple cloning site. The fragments were put together byknown cloning techniques, e.g. filling in of sticky ends with Klenow,adapter cloning, etc. All data were derived from Genbank®, NationalNucleic Acid Sequence Data Bank, NIH, USA.

pGBSCC-3 was derived by molecular cloning in E. coli JM101 of theKpnI/SphI P₄₅₀SCCcDNA insert of pGBSCC-2 (described in Example 1) intothe appropriate sites in pBHA-1 as indicated in FIG. 6.

By molecular cloning in E. coli JM101, the methionine initiation codonwas introduced by exchanging the StuI/SphI (SEQ ID NO: 6) fragment inpGBSCC-3 by a synthetically derived SphI/StuI fragment.

SPH  1                   STU  1      CATATGATCAGTACTAAGACCCCTAGG (SEQ IDNO:4)  GTACGTATACTAGTCATGATTCTGGGGATCC (SEQ ID NO:5)      NDE  1

containing an Ndel site at the ATG initiation codon. The obtainedplasmid pGBSCC-4 is shown in FIG. 7. The “Hpa II” Bacillus promoter wasintroduced upstream of P₄₅₀SCCcDNA sequences by digestion of the E. colipart of the shuttle plasmid by agarose gel electrophoresis andsubsequent religation and transformation into Bacillus subtilis 1A40(BGSC 1A40) competent cells. Neomycin resistant colonies were analyzedand the plasmid pGBSCC-5 (FIG. 8) was obtained. Expression of bovineP₄₅₀SCC was studied by preparing a cellular protein fraction of anovernight culture at 37° C. in TSB medium (Gibco) containing 10 μg/ml ofneomycin. Cells of 100 μl of culture, containing approximately 5.10⁶cells, were harvested by centrifugation and resuspended in 10 mMTris/HCl pH 7.5. Lysis was performed by adding lysozyme (1 mg/ml) andincubation during 15 minutes at 37° C. After treatment with 0.2 mgDNase/ml during 5 minutes at 37° C., the mixture was adjusted to 1×SBbuffer, as described by Laemmli, Nature, Vol. 227, pp. 680-685, 1970, ina final volume of 200 μl. After heating for 5 minutes at 100° C., 15 μlof the mixture was subjected to a 7.5% of SDS/polyacrylamide gelelectrophoresis. As shown in FIG. 9 (lane C), a 53 kDa band could bedetected after immunoblotting of the gel probed with P₄₅₀SCC specificantibodies. Specific bovine P₄₅₀SCC antibodies were obtained byimmunization of rabbits with purified P₄₅₀SCC protein isolated frombovine adrenal cortex tissue.

EXAMPLE 3 Expression of P₄₅₀SCC in the Bacterial Host Bacilluslicheniformis

Expression of bovine P₄₅₀SCC in B. licheniformis was performed bytransformation plasmid pGBSCC-5 into the appropriate host strain B.licheniformis T5 (CBS 470.83). A cellular protein fraction prepared asdescribed in Example 2, from an overnight culture at 37° C. in TryptonSoy Broth (TSB) medium (Oxoid) containing 10 μg/ml of neomycin, wasanalyzed by SDS/PAGE and Western-blotting. As shown in FIG. 9 (lane f),a 53 kDa sized protein band was visualized after incubation of thenitrocellulose filter with antibodies specific for bovine P₄₅₀SCC. Onetransformant, SCC-201, was further analyzed for in vivo activity ofP₄₅₀SCC (see Example 11).

EXAMPLE 4 Expression of P₄₅₀SCC in the Bacterial Host Escherichia Coli

(a) Construction of the Expression Cassette

To derive a suitable expression vector in the host E. coli for bovineP₄₅₀SCC, pTZ18R was mutated by site-directed mutagenesis as described byZoller et al. (Methods in Enzymology, Vol. 100, pp. 468-500, 1983);Zoller et al. (Methods in Enzymology; Vol. 154, 329-350, 1987) andKramer et al.(Methods in Enzymology, Vol. 154, pp. 350-367, 1987).Plasmids and strains for in vitro mutagenesis experiments were obtainedfrom Pharmacia Inc.

A synthetic derived oligomer with the sequence:

5′-CAG  GAA  ACA  CAT  ATG  ACC  ATG  ATT-3′ (SEQ ID NO:7)                 |        |                    NdeI

was used to create an NdeI restriction site at the ATG initiation codonof the lac Z gene in pTZ18R. The resulting plasmid pTZ18RN was digestedwith NdeI and KpnI and the NdeI/KpnI DNA fragment of pGBSCC-4 containingthe full-length SCCcDNA, was inserted by molecular cloning as indicatedin FIG. 10. The transcription of P₄₅₀SCCcDNA sequences in the derivedplasmid pGBSCC-17 will be driven by the E. coli lac-promoter.

(b) Expression of P₄₅₀SCC in the Host E. coli JM101

pGBSCC-17 was introduced into E. coli JM101 competent cells by selectingampicillin resistant colonies. Expression of cytochrome P₄₅₀SCC wasstudied by preparing a cellular protein fraction (described in Example2) of transformants SCC-301 and 302 from an overnight culture at 37° C.in 2×TY medium (containing per liter of de-ionized water: Bacto tryptone(Difco), 16 g; yeast extract (DiFco), 10 g and NaCl, 5 g) containing 50μg/ml of ampicillin.

Protein fractions were analyzed by SDS/PAGE stained with Coomassiebrilliant blue (FIG. 11A) or by Western-blot and probed, with antibodiesspecific for bovine P₄₅₀SCC (FIG. 11B). Both analyses show a protein ofthe expected length (FIG. 11A, lanes 1 and 2 and in FIG. 11B, lanes 3and 4) for the transformants SCC-301 and SCC-302, resp., which is absentin the E. coli JM101 control strain (FIG. 11A, lane 3 and FIG. 11B, lane2).

EXAMPLE 5 Construction, Transformation and Expression of P₄₅₀SCC in theYeast Kluyveromyces lactis

(a) Introduction of the Geneticin Resistance Marker in pUC19

A DNA fragment comprising the Tn5 gene (Reiss et al., EMBO J., Vol. 3,pp. 3317-3322, 1984) conferring resistance to geneticin under thedirection of the alcohol dehydrogenase I (ADHI) promoter from S.cerevisiae, similar to that described by Bennetzen et al. (J. Biol.Chem., Vol. 257, pp. 3018-3025, 1982) was inserted into SmaI site ofpUC19 (Yanisch-Perron et al., Gene., Vol. 33, pp. 103-119, 1985). Theobtained plasmid, pUCG418, is shown in FIG. 12.

E. coli containing pUCG418 was deposited at Centraal Bureau voorSchimmelcultures under CBS 872.87.

(b) Construction of the Expression Cassette

A vector was constructed, comprising pUCG418 (for description seeExample 5(a)) cut with XbaI and HindIII, the XbaI-SalI fragment frompGB901 containing the lactase promoter (see van den Berg et al.,Continuation-in-part of U.S. patent application Ser. No. 572,414:Kluyveromyces as a host strain) and synthetic DNA comprising part of the3′ noncoding region of the lactase gene of K. lactis. This plasmid,pGB950, is depicted in FIG. 13. pGB950 was cut with SalI and XhoI andsynthetic DNA was inserted:

SAL  1                     STU  1                XHo  1 TCGACAAAAATGATCAGTACAGTACTAAGACTCCTAGGCCTATCGATTC (SEQ ID NO:9)     GTTTTTACTAGTCATGATTCTGAGGATCCGGATAGCTAAGAGCT (SEQ ID NO:10)

resulting in plasmid pGBSCC-6 as shown in FIG. 13.

The StuI-EcoRI fragment from pGBSCC-2 (see Example 1) containing theP₄₅₀SCC coding region was isolated and the sticky end was filled in,using Klenow DNA polymerase. This fragment was inserted into pGBSCC-6cut with StuI. The plasmid containing the fragment in the correctorientation was called pGBSCC-7 (see FIG. 14).

(c) Transformation of K. lactis

K. lactis strain CBS 2360 was grown in 100 ml of YEPD-medium (1% yeastextract, 2% peptone, 2% glucose-monohydrate) containing 2.5 ml of 6.7%(w/w) yeast nitrogen base (Difco laboratories) solution to an 0D₆₁₀ ofabout 7. From 10 ml of the culture, the cells were collected bycentrifugation, washed with TE-buffer (10-mM Tris-HCl pH 7.5; 0.1 mMEDTA) and resuspended in 1 ml of TE-buffer. An equal volume of 0.2 Mlithium acetate was added and the mixture was incubated for 1 hour at30° C. in a shaking waterbath. 15 μg of pGBSCC-7 was cut at the uniqueSacII site in the lactase promoter, ethanol precipitated and resuspendedin 15 μl of TE-buffer. This DNA preparation was added to 100 μl of thepre-incubated cells and the incubation was prolonged for 30 minutes.Then, an equal volume of 70% PEG 4000 was added and the mixture wasincubated for 1 hour at the same temperature, followed by a heat shockof 5 minutes at 42° C. Then, 1 ml of YEPD-medium was added and the cellswere incubated for 90 minutes in a shaking waterbath of 30° C. Finally,the cells were collected by centrifugation, resuspended in 300 μl ofYEPD and spread on agar plates containing 15 ml of YEPD agar with 300μg/ml of geneticin and were overlayered 1 hour before use with 15 ml ofYEPD-agar without G418. Colonies were grown for 3 days at 30° C.

(d) Analysis of the Transformants

Transformants and the control strain CBS 2360 were grown in YEPD mediumfor about 64 hours at 30° C. The cells were collected by centrifugation,resuspended in a physiological salt solution of an 0D₆₁₀ of 300 anddisrupted by shaking with glass beads for 3 minutes on a Vortex shakerat maximum speed. Cell debris was removed by centrifugation for 10minutes at 4500 rpm in a Hearaeus Christ minifuge GL. From thesupernatants, 40 μl samples were taken for analysis on immunoblots (seeFIG. 15A, lane 3 and FIG. 15B, lane 4).

The results show that a protein of the expected length is expressed inK. lactis cells transformed with pGBSCC-7. The transforman was denotedas K. lactis SCC-101.

EXAMPLE 6 Construction, Transformation and Expression of P₄₅₀SCC in theYeast Saccharomyces Cerevisiae

(a) Construction of the Expression Cassette

To delete the lactase promoter, pGB950 (see Example 4(b)) was cut withXbaI and SalI and the sticky ends were filled in using Klenow DNApolymerase and subsequently ligated. In the resulting plasmid, pGBSCC-8,the XbaI-site was destroyed, but the SalI site was maintained.

The SalI-fragment from pGB161 (see J. A. van den Berg et al., EuropeanPatent No. 96,430) containing the isocytochrome CI (cyc 1) promoter fromS. cerevisiae was isolated and partially digested with XhoI. The 670 bpXhoI-SalI fragment was isolated and cloned into the SalI-site ofpGBSCC-8. In the selected plasmid, pGBSCC-9, the SalI-site between thecyc 1 promoter and the 3′ noncoding region of the lactase gene wasmaintained (FIG. 16) (HindIII partially digested).

The SalI-HindIII fragment from pGBSCC-7, containing the P₄₅₀SCC codingregion was inserted in pGBSCC-9 cut with SalI and HindIII. In theresulting plasmid, pGBSCC-10, the P₄₅₀SCC coding region was downstreamto the cyc 1 promoter (FIG. 17).

(b) Transformation of S. cerevisiae

S. cerevisiae strain D273-10B (ATCC 25657) was grown in 100 ml of YEPDovernight at 30° C., subsequently diluted (1:10000) in fresh medium andgrown to an 0D₆₁₀ of 6. The cells from 10 ml of the culture werecollected by centrifugation and suspended in 5 ml of TE-buffer. Again,the cells were collected by centrifugation, suspended in 1 ml of theTE-buffer and 1 ml of 0.2 M lithium acetate was added. The cells wereincubated for 1 hour in a shaking waterbath at 30° C. 15 μg of pGBSCC-10were cut at the unique MluI-site in the cyc 1 promoter, ethanolprecipitated and resuspended in 15 μl of TE. This DNA preparation wasadded to 100 μl of the pre-incubated yeast cells and incubated (shaking)for 30 minutes at 30° C. After addition of 115 μl of a 70% PEG4000solution, the incubation was prolonged 60 minutes without shaking.Subsequently, a heat shock of 5 minutes at 42° C. was given to the cellsand 1 ml of YEPD medium was added, followed by an one and one-half hourincubation at 30° C. in a shaking waterbath. Finally, the cells werecollected by centrifugation, resuspended in 30 μl of YEPD and spread onYEPD agar plates containing geneticin (300 μg/ml). Colonies were grownfor three days at 30° C.

(c) Analysis of the Transformants

Transformants and the control strain were grown in YEPL-medium (1% yeastextract, 2% bactopeptone, 3.48% K₂HPO₄ and 2.2% of a 90% L-(+)-lacticacid solution; before sterilization, the pH was adjusted to 6.0 using a25% ammonia solution) for 64 hours at 30° C. Further analysis was doneas described in Example 5(d). The immunoblot-analysis demonstrated theexpression of P₄₅₀SCC in S. cerevisiae (FIG. 15A, lane 1).

EXAMPLE 7 Construction, Transformation and Expression of Pre-P₄₅₀SCCEncoding DNA in the Yeast Kluyveromyces lactis

(a) Construction of the Expression Cassette

Plasmid pGB950 (see Example 5(b)) was cut with SalI and XhoI andsynthetic DNA was inserted:

SAL  I  TCGACAAAAATGTTGGCTCGAGGTTTGCCATTGAGATCCGCTTTGGTTAAGGCTTGTCC     GTTTTTACAACCGAGCTCCAAACGGTAACTCTAGGCGAAACCAATTCCGAACAGGACCAATCTTGTCCACTGTTGGTGAAGGTTGGGGTCACCACAGAGTTGGTACTGGTGAAGGTGGTTAGAACAGGTGACAACCACTTCCAACCCCAGTGGTGTCTCAACCATGACCACTTCC                         STU  1       XHO  1TGCTGGTATCAGTACTAAGACTCCTAGGCCTATCCATTC (SEQ ID NO:11)ACGACCATAGTCATGATTCTGAGGATCCCGATACCTAAGAGCT (SEQ ID NO:12)

resulting in plasmid pGBSCC-11 (FIG. 18). Analogous as described inExample 5(b), the P₄₅₀SCC coding region of pGBSCC-2 was inserted intopGBSCC-11 cut with StuI. The plasmid containing the fragment in thecorrect orientation was called pGBSCC-12 (FIG. 18).

(b) Transformation of K. lactis and Analysis of the Transformants

Transformation of K. lactis with pGBSCC-12 was performed as described inExample 5(c). The transformants were analyzed as described in Example5(d). The analysis demonstrated the production of P₄₅₀SCC by K. lactis(FIG. 15B, lane 3).

EXAMPLE 8 Construction, Transformation and Expression of Pre-P₄₅₀SCCEncoding DNA in the Yeast Saccharomyces cerevisiae

(a) Construction of the Expression Cassette

The SalI-HindIII (HindIII partially digested) fragment from pGBSCC-12containing the pre-P₄₅₀SCC coding region was inserted in pGBSCC-9 cutwith SalI and HindIII. The resulting plasmid was called pGBSCC-13 (FIG.19).

(b) Transformation of S. cerevisiae and Analysis of the Transformants

S. cerevisiae strain D273-10B was transformed with pGBSCC-13 asdescribed in Example 6(b). The transformants were analyzed as describedin Example 5(c). The result, shown in FIG. 15C (lane 3), demonstratedthe expression of P₄₅₀SCC by S. cerevisiae. One transformant, SCC-105,was further analyzed for in vitro activity of P₄₅₀SCC (see Example 12).

EXAMPLE 9 Construction, Transformation and Expression in Kluyveromyceslactis of P ₄₅₀SCC Sequences Fused to the Pre-region of CytochromeOxidase VI from Saccharomyces cerevisiae

(a) Construction of the Expression Cassette

Plasmid pGB950 (see Example 6(b)) was cut with SalI and XhoI andsynthetic DNA was inserted:

SAL  I  TCGACAAAAATGTTGTCTCGAGCTATCTTCAGAAACCCAGTTATCAACAGAACTTTGTT     GTTTTTACAACAGAGCTCGATAGAAGTCTTTGGGTCAATAGTTGTCTTGAAACAAGAGAGCTAGACCAGGTGCTTACCACGCTACTAGATTGACTAAGAACACTTTCATCCAATCCTCTCGATCTCGTCCACGAATGGTGCGATGATCTAACTGATTCTTGTGAAAGTAGGTTAG                            STU  1       XHO  1CAGAAAGTACATCAGTACTAAGACTCCTAGGCCTATCGATTC (SEQ ID NO:13)GTCTTTCATGTAGTCATGATTCTGAGGATCCGGATACCTAAGAGCT (SEQ ID NO:14)

resulting in plasmid pGBSCC-14.

The amino acid sequence from the cytochrome oxidase VI (COX VI)pre-sequence was taken from the article of Wright et al. (J. Biol.Chem., Vol. 259, pp. 15401-15407, 1984). The synthetic DNA was designed,using preferred yeast codons. The P₄₅₀SCC coding region of pGBSCC-2 wasinserted into pGBSCC-14 cut with StuI, similarly as described in Example5(b). The plasmid containing the P₄₅₀SCC coding sequence in frame withthe COX VI pre-sequence was called pGBSCC-15 (FIG. 20).

(b) Transformation of K. lactis and Analysis of the Transformants

Transformation of K. lactis with pGBSCC-15 was performed as described inExample 5(c). The transformants were analyzed as described in Example5(d). The result (FIG. 15B, lane 2) shows that P₄₅₀SCC was expressed.

EXAMPLE 10 Construction, Transformation and Expression in Saccharomycescerevisiae of P₄₅₀SCC Sequences Fused to the Pre-region of CytochromeOxidase VI from Saccharomyces cerevisiae

(a) Construction of the Expression Cassette

The SalI-HindIII (HindIII partially digested) fragment from pGBSCC-15,containing the coding region for P₄₅₀SCC fused to the COX VIpre-sequence, was inserted in pGBSCC-9 cut with SalI and HindIII. Theresulting plasmid was called pGBSCC-16 (FIG. 21).

(b) Transformation of S. cerevisiae and Analysis of the Transformants

S. cerevisiae strain D273-10B was transformed with pGBSCC-16 asdescribed in Example 6(b). The transformants were analyzed as describedin Example 6(c). The result, shown in FIG. 15C (lane 2), demonstratedthe expression of P₄₅₀SCC by S. cerevisiae.

EXAMPLE 11 In vivo Activity of P₄₅₀SCC in Bacillus licheniformis SCC-201

B. licheniformis SCC-201 was obtained as described in Example 3 and theorganism was inoculated in 100 ml of medium A. Medium A consisted of:

Calcium chloride-hexahydrate 1 g Ammonium sulfate 5 g Magnesiumchloride-hexahydrate 2.25 g Manganese sulfate-tetrahydrate 20 mg Cobaltchloride-hexahydrate 1 mg Citric acid-monohydrate 1.65 g Distilled water600 ml Trace elements stock solution 1 ml Antifoam (SAG 5693) 0.5 mgTrace elements stock solution contained per 1 of distilled water:CuSO₄.5H₂O 0.75 g H₃BO₃ 0.60 g KI 0.30 g FeSO₄(NH₄)₂SO₄.2H₂O 27 gZnSO₄.7H₂O 5 g Citric acid.H₂O 15 g MnSO₄.H₂O 0.45 g Na₂MoO₄.H₂O 0.60 gH₂SO₄ (96%) 3 ml

After sterilization and cooling to 30° C. to complete the medium, 60 gof maltose-monohydrate dissolved in 200 ml of distilled water(sterilized 20 minutes, 120° C.), 200 ml 1 M of potassium phosphatebuffer (pH 6.8; sterilized 20 minutes, 120° C.) and 1.7 g of YeastNitrogen base (Difco) dissolved in 100 ml of distilled water (sterilizedby membrane filtration) were added to the medium. The culture was grownfor 64 hours at 37° C. and subsequently 2 ml of this culture were addedas inoculum to 100 ml of medium A containing 10 mg of cholesterol.Cholesterol was added as a solution containing cholesterol 10 mg;Tergitol™/ethanol (1:1, v/v), 0.75 ml and Tween 80™, 20 μl. The culturewas grown for 48 hours at 37° C., whereupon the culture was extractedwith 100 ml of dichloromethane. The mixture was separated bycentrifugation and the organic solvent layer was collected. Theextraction procedure was repeated twice and the 3×100 ml ofdichloromethane fractions were pooled. The dichloromethane wasevaporated by vacuum distillation and the dried extract (approximately450 mg) was analyzed for pregnenolone using a gas chromatograph-massspectrometer combination.

GC-MS Analysis.

From the dried extract, a defined amount was taken and silylated byadding a mixture of pyridine bis-(trimethyl-silyl)-trifluoroacetamideand trimethylchlorosilane. The silylated sample was analyzed by aGL-MS-DS combination (Carlo Erba MEGA 5160-Finnigan MAT 311A-Kratos DS90) in the selected ion mode. Gas chromatography was performed under thefollowing conditions: injection moving needle at 300° C.; columnM.cpsil29 0.25 inner diameter of df 0.2 μm operated at 300° C. isotherm;direct introduction into MS-source.

Samples were analyzed by monitoring ions m/z 298 from pregnenolone at aresolution of 800. From the measurements, it was clear that in the caseof the host strain B. licheniformis T5, no pregnenolone could bedetected (detection limit 1 picogram), whereas in the case of B.licheniformis SCC-201, production of pregnenolone easily could bemonitored.

EXAMPLE 12 In vivo Activity of P₄₅₀SCC from Saccharomyces cerevisiaeSCC-105

S. cerevisiae SCC-105 was obtained, as described in Example 8 and theorganism was inoculated in 100 ml of medium B. Medium B contained perliter of distilled water:

Yeast extract 10 g Bacto Peptone (Oxoid) 20 g Lactic acid (90%) 20 gDipotassium phosphate 35 g pH = 5.5 (adjusted with ammonia, 25% w/w)

This culture was grown for 48 hours at 30° C. and subsequently, thisculture was used as inoculum for a fermentor containing medium C. MediumC consisted of:

Yeast extract 100 g Bacto Peptone (Oxoid) 200 g Lactic acid (90%) 220 mlDipotassium hydrogen phosphate 35 g Distilled water 7800 ml pH wasadjusted at pH = 6.0 with ammonia (25%) and the fermentor including themedium was sterilized (1 hour, 120° C.).

After cooling, 2.4 g of geneticin dissolved in 25 ml of distilled waterwere sterilized by membrane filtration and added to the medium. Theinoculated mixture was grown in the stirred reactor (800 rpm) at 30° C.,while sterile air was passed through the broth at a rate of 300 l/h andthe pH was automatically kept at 6.0 with 4N H₂SO₄ and 5% NH₄OH (5%NH₄OH in distilled water; sterilized by membrane filtration). After 48hours, a feed of lactic acid (90%, sterilized by membrane filtration)was started at a rate of 20 g/h. The fermentation was then resumed for40 hours, whereupon the cells were collected by centrifugation (4,000×g,15 minutes).

The pellet was washed with 0.9% (w/w) NaCl, followed by centrifugation(4000×g, 15 minutes); the pellet washed with phosphate buffer (50 mM, pH=7.0) and cells were collected by centrifugation (4,000×g, 15 minutes).The pellet was taken up in phosphate buffer (50 mM, pH=7.0) resulting ina suspension of 0.5 g wet weight/ml. This suspension was treated in aDyno^(R)-mill (Willy A. Bachofen Maschinenfabrik, Basel, Schweiz).Unbroken cells were removed by centrifugation (4,000×g, 15 minutes). Thecells-free extract (2250 ml, 15-20 mg protein/ml) was stored at −20° C.

P₄₅₀SCC was roughly purified by the following procedure. From 50 ml ofthawed cell-free extract, a rough membrane fraction was pelleted byultracentrifugation (125,000×g, 30 minutes) and resuspended in 50 ml ofa 75 mM potassium phosphate solution (pH 7.0), containing 1% of sodiumcholate. This dispersion was gently stirred for 1 hour at 0° C., andsubsequently centrifugated (125,000×g, 60 minutes). To the thus obtainedsupernatant containing solubilized membrane proteins, (NH₄)₂SO₄ wasadded (30% w/v), while the pH was kept at 7.0 by adding small amounts ofNH₄OH solution (6N). The suspension was stirred for 20 minutes at 0° C.,after which the fraction of precipitated proteins was collected bycentrifugation (15,000×g, 10 minutes). The pellet was resuspended in 2.5ml with 100 mM potassium phosphate buffer (pH 7.0) containing 0.1 mMdithio-threitol and 0.1 mM EDTA. This suspension was eluted over a gelfiltration column (PD10, Pharmacia), yielding 3.5 ml of a desaltedprotein fraction (6 mg/ml), which was assayed for P₄₅₀SCC activity.

P₄₅₀SCC activity was determined by an assay which was essentially basedon a method of Doering (Methods Enzymology, Vol. 15, pp. 591-596, 1969).The assay mixture consisted of the following solutions:

Solution A (natural P₄₅₀SCC electron donating system): a 10 mM potassiumphosphate buffer (pH 7.0) containing 3 mM of EDTA, 3 mM ofphenylmethylsulfonyl fluoride (PMSF), 20 μM of adrenodoxin and 1 μM ofadrenodoxin reductase (electron carriers; both purified from bovineadrenal cortex), 1 mM of NADPH (electron donor) and 15 mMglucose-6-phosphate and 8 units/ml of glucose-6-phosphate-dehydrogenase(NADPH generating systems).

Solution B (substrate): a micellar solution of 37.5 μM cholesterol(doubly radiolabeled with [26,27-¹⁴C] cholesterol (40 Ci/mol) and[7α-³H] cholesterol (400 Ci/mol)) in 10% (v/v) Tergitol™ NP40/ethanol(1:1, v/v).

The assay was started by mixing 75 μl of solution A with 50 μl ofsolution B and 125 μl of the roughly purified P₄₅₀SCC fraction (orbuffer as reference). The mixture was stirred gently at 30° C. Samples(50 μl) were drawn after 0, 30 and 180 minutes and diluted with 100 μlof water. Methanol (100 μl) and chloroform (150 μl) were added to thediluted sample. After extraction and centrifugation (5,000×g, 2minutes), the chloroform layer was collected and dried. The dry residuewas dissolved in 50 μl of acetone containing 0.5 mg of a steroid mixture(cholesterol, pregnenolone and progesterone (1:1:1, w/w/w) andsubsequently, 110 μl of concentrated formic acid were added. Thesuspension was heated for 15 minutes at 120° C. Then, the ¹⁴C/³H ratiowas determined by double label liquid scintillation counting. This ratiois a direct measure for the side chain cleavage reaction because the¹⁴C-labeled side chain was evaporated from the mixture as isocaprylicacid during the heating procedure.

Using this assay, it was found that the P₄₅₀SCC fraction, roughlypurified from S. cerevisiae SCC-105, showed side chain cleavageactivity. During 3 hours of incubation, 45% of the cholesterol had beenconverted. By means of thin layer chromatography, the reaction productwas identified as pregnenolone.

EXAMPLE 13 Molecular Cloning of a Full-length cDNA Encoding the BovineCytochrome P₄₅₀ Steroid 17α-Hydroxylase (P₄₅₀17α)

Approximately 10⁶ pfu's of the bovine adrenal cortex cDNA librarydescribed in Example 1 were selected for P₄₅₀17αcDNA sequences byscreening with two ³²P-end labeled synthetic oligomers specific forP₄₅₀cDNA. Oligomer 17α-1 (5′-AGT GGC CAC TTT GGG ACG CCC AGA GAA TTC-3′(SEQ ID NO: 15)) and oligmer 17α-2 (5′-GAG GCT CCT GGG GTA CTT GGC ACCAGA GTG CTT GGT-3′ (SEQ ID NO: 16)) are complementary to the bovineP₄₅₀SCCcDNA sequences as described by Zuber et al. (J. Biol. Chem., Vol.261, pp. 2475-2482, 1986) from position 349 to 320 and 139 to 104,respectively.

Selection with oligomer 17α-1 revealed ±1500 hybridizing pfu's. Severalhybridizing pfu's were selected, purified and scaled up for preparativephage DNA isolation. The EcoRI site inserts of the recombinantlambda-gt11 DNA's were subcloned in the EcoRI site of pTZ18R. One clone,pGB17α-1, was further characterized by restriction endonuclease mappingand DNA-sequencing. Plasmid pGB17α-1 contained an 1.4 kb EcoRI insertcomplementary to the 3 part of P₄₅₀17α from the EcoRI site at position320 to the polyadenylation site at position 1721 as described by Zuberet al. A map of pGB17α-1 is shown in FIG. 22A.

Eight hybridizing pfu's were obtained by selecting the cDNA library witholigomer 17α-2. After purification, upscaling of recombinant phages andisolation of rec lambdagt11 DNA's, EcoRI inserts were subcloned in theEcoRI site of pTZ18R. EcoRI inserts varied in length from 270 bp to 1.5kbp. Only one clone, pGB17α-2 containing a 345 bp EcoRI-fragment, wasfurther investigated by nucleotide sequencing and compared with thepublished P₄₅₀17αcDNA sequence data by Zuber et al. As shown in FIG.22B, the P₄₅₀17αcDNA sequence in pGB17α-2 started 72 bp upstream thepredicted AUG start codon at position 47 and showed complete homologywith the 5′ part of P₄₅₀17αcDNA till the EcoRI site at position 320 asdescribed by Zuber et al.

A full-length bovine P₄₅₀17αcDNA was constructed by molecular cloning inE. coli JM101 of a ligation mixture containing a partial EcoRI digest ofpGB17α-1 and the 345 bp EcoRI fragment of pGB17α-2. The obtained clonepGB17α-3 contained a full-length bovine P₄₅₀17αcDNA and is shown in FIG.22C.

EXAMPLE 14 Construction and Transformation of a Full-length P₄₅₀17αc-DNAClone Into the Yeast Kluyveromyces lactis

(a) Construction of the Expression Vector

To derive a suitable expression vector in yeast hosts for bovineP₄₅₀17α, pGB17α-3 was mutated by site-directed mutagenesis as describedby Zoller et al, (Methods in Enzymology, Vol. 100, pp. 468-500, 1983);Zoller et al. (Methods in Enzymology, Vol. 154, 329-350, 1987) andKramer et al. (Methods in Enzymology Vol. 154, pp. 350-367, 1987).Plasmids and strains for in vitro mutagenesis experiments were obtainedfrom Pharmacia Inc.

As indicated in FIG. 23, 9 bp just upstream the ATG initiation codonwere changed to obtain a SalI restriction site and optimal yeasttranslation signals using the synthetic oligomer 17α-3

(SEQ ID NO:18)                         SAL  15′-TCTTTGTCCTGACTGCTGCCAGTCGACAAAAATGTGGCTGCTC-3′

The resulting plasmid, pGB17α-4, was digested with SalI and SmaI and theDNA-fragment containing the full length P₄₅₀17αcDNA was separated byelectrophoresis, isolated and transferred by molecular cloning in E.coli JM101 into the pGB950 vector (see Example 5) which was firstdigested with XhoI, sticky ends filled in with Klenow DNA polymerase andsubsequently digested with SalI, resulting in the plasmid pGB17α-5 asdepicted in FIG. 24.

(b) Transformation of K. lactis

15 μg of pGB17α-5, cut at the unique SacII site in the lactase promoter,was used to transform K. lactis strain CBS 2360 as indicated in Example5. Transformants were analyzed for the presence of integrated pGB17α-5sequences in the host genome by southern analysis. One transformant,17α-101 containing at least three copies of pGB17αa-5 in the genomichost DNA, was further analyzed for in vivo activity of P₄₅₀17α (seeExample 16).

EXAMPLE 15 Construction and Transformation of P₄₅₀17α in the BacterialHosts Bacillus subtilis and Bacillus licheniformis

(a) Construction of the Expression Vector

To derive a suitable expression vector in Bacillus hosts for bovineP₄₅₀17α, pGB17α-3 was mutated by site-directed mutagenesis as describedin Example 14. As indicated in FIG. 25, an NdeI restriction site wasintroduced at the ATG initiation codon using the synthetic oligomer17α-4:

5′-GCT  GCC  ACC  CAG  ACC  ATA  TGT  GGC  TGC  TCC  T-3′ (SEQ ID NO:20)                         |        |                           NdeI

The resulting plasmid, pGB17α-6, was partially digested with EcoRI. TheDNA fragment containing the full-length P₄₅₀17αcDNA was separated by gelelectrophoresis, isolated and ligated to EcoRI digested pBHA-1 DNA asshown in FIG. 26. The ligate was molecular cloned by transferring theligation mixture into E. coli JM101 to obtain pGB17α-7.

(b) Transformation of B. subtilis and B. licheniformis

The “HpaIII” Bacillus promoter was introduced upstream of theP₄₅₀17αcDNA sequences by digestion with pGB17α-6 with the restrictionenzyme NdeI, separation of the E. coli part of the shuttle plasmid byagarose gel electrophoresis and subsequent religation and transformationof B. subtilis 1A40 (BGSC 1A40) competent cells. Neomycin resistantcolonies were analyzed and the plasmid pGB17α-8 (FIG. 27) was obtained.

Transformation of the host B. licheniformis T5 (CBS 470.83) was alsoperformed with pGB17α-8. The plasmid remained stable in the appropriateBacillus hosts as revealed by restriction analysis of pGB17α-8, evenafter many generations.

EXAMPLE 16 In vivo Activity of P₄₅₀17α in Kluyveromyces lactis 17α-101

K. lactis 17α-101 was obtained as described in Example 14. The organismwas inoculated in 100 ml of medium D. Medium D contained per liter ofdistilled water:

Yeast Extract (Difco) 10 g Bacto Peptone (Oxoid) 20 g Dextrose 20 g

After sterilization and cooling to 30° C., 2.68 g of Yeast Nitrogen Base(Difco) dissolved in 40 ml of distilled water (sterilized by membranefiltration) and 50 mg of neomycin dissolved in 1 ml of distilled water(sterilized by membrane filtration) were added to the medium.Subsequently, 50 mg of progesterone dissolved in 1.5 ml ofdimethylformamide were added to 100 ml of medium. The culture was grownfor 120 hours at 30° C. and subsequently, 50 ml of culture broth wereextracted with 50 ml of dichloromethane. The mixture was centrifugatedand the organic solvent layer was separated. Dichloromethane wasevaporated by vacuum distillation and the dried extract (about 200 mg)was taken up in 0.5 ml of chloroform. This extract contained17α-hydroxyprogresterone as shown by thin layer chromatography. Thestructure of the compound was confirmed by H-MNR and ¹³C-NMR. NMRanalysis also showed that the ratio of17α-hydroxyprogesterone/progesterone in the extract was approximately0.3.

EXAMPLE 17 Molecular Cloning of a Full-length cDNA Encoding the BovineCytochrome P₄₅₀ Steroid 21-Hydroxylase (P₄₅₀C21)

Approximately 10⁶ pfu's of the bovine adrenal cortex cDNA library,prepared as described in Example 1, were hybridized with a ³²P-endlabeled oligo C21-1. This oligo containing the sequence 5′-GAT GAT GCTGCA GGT AAG CAG AGA GAA TTC-3′ (SEQ ID NO: 21) was a specific probe forthe bovine P₄₅₀C21 gene located downstream the EcoRI site in the P₄₅₀C21cDNA sequence as described by Yoshioka et al. (J. Biol. Chem., Vol. 261,pp. 4106-4109, 1986). From the screening, one hybridizing pfu wasobtained. The EcoRI insert of this recombinant lambda-gt11 DNA wassubcloned in the EcoRI site of pTZ18R resulting in a construct calledPGBC21-1. As shown in FIG. 28, this plasmid contains a 1.53 kb EcoRIinsert complementary to the P₄₅₀C21cDNA sequences from the EcoRI site atposition 489 to the polyadenylation site as described by Yoshioka etal., as revealed by nucleotide sequencing.

To isolate the remaining 5′ part (490 bp) of the P₄₅₀C21cDNA, a newbovine adrenal cortex cDNA library was prepared with the proceduredescribed in Example 1 with only one modification. As primer for thefirst cDNA strand synthesis, an additional oligomer C21-2 was added.Oligomer C21-2 with the nucleotide sequence 5′-AAG CAG AGA GAA TTC-3′(SEQ ID NO: 22) was positioned downstream from the EcoRI-site ofP₄₅₀C21cDNA from position 504 to 490.

Screening of this cDNA library with a ³²P-end labeled oligomer C21-3containing the P₄₅₀C21 specific sequence 5′-CTT CCA CCG GCC CGA TAG CAGGTG AGC GCC ACT GAG-3′ (SEQ ID NO: 23) (positions 72 to 37) revealedapproximately 100 hybridizing pfu's. The EcoRI-insert of only onerecombinant lambda-gt11 DNA was subcloned in the EcoRI-site of PTZ18Rresulting in a construct called PGBC21-2. This plasmid (FIG. 28)contained an insert of 540 bp complementary to the P₄₅₀C21 cDNAsequences from position −50 to the EcoRI-site at position 489 asrevealed by nucleotide sequencing.

EXAMPLE 18 Construction of a P₄₅₀C21cDNA Bacillus Expression Vector andTransformation to the Bacterial Hosts Bacillus subtilis and Bacilluslicheniformis

(a) Construction of the Expression Vector

To construct a full-length P₄₅₀C21cDNA with flanking sequences specificfor the Bacillus expression vector pBHA-1, the 5′ part of the P₄₅₀C21gene was first modified by the Polymerase Chain Reaction (PCR) methodwith pGBC21-2 as template and two specific P₄₅₀C21-oligomers as primers.Oligomers C21-4 (5′-CTC ACT GAT ATC CAT ATG GTC CTC GCA GGG CTG CTG-3′(SEQ ID NO: 24)) contained 21 nucleotides complementary to C21-sequencesfrom positions 1 to 21 and 18 additional bases to create an EcoRVrestriction site and an NdeI restriction site at the ATG initiationcodon. Oligomer C21-5 (5′-AGC TCA GAA TTC CTT CTG GAT GGT CAC-3′ (SEQ IDNO: 25)), was 21 bases complementary to the minus strand upstream theEcoRI-site at position 489.

The PCR was performed as described by Saiki et al (Science, Vol. 239,pp. 487-491, 1988) with minor modifications. The PCR was performed in avolume of 100 μl containing: 50 mM KCl, 10 mM Tris-HCl pH 8.3, 1.5 mMMgCl₂, 0.01% (w/v) gelatin, 200 μM each dNTP, 1 μM each C21-primer and10 ng pGBC21-2 template. After denaturation (7′ at 100° C.) and additionto 2 U of Taq-polymerase (Cetus), the reaction mixture was performed to25 amplification cycles (each: 2′ at 55° C., 3′ at 72° C., 1′ at 94° C.)in a DNA-amplifier apparatus (Perkin-Elmer). In the last cycle, thedenaturation step was omitted. A schematic view of this P₄₅₀C21cDNAamplification is shown in FIG. 29.

The amplified fragment was digested with EcoRV and EcoRI and inserted bymolecular cloning into the appropriate sites of pSP73 (Pronega). Theobtained plasmid was called pGBC21-3. As shown in FIG. 30, the 3′P₄₅₀C21-EcoRI fragment of pGBC21-1 was inserted in the right orientationinto the EcoRI-site of pGBC21-3. The obtained vector pGBC21-4 wasdigested with EcoRV and KpnI (KpnI was situated in the multiple cloningsite of pSP73) and the fragment containing the full-length P₄₅₀C21cDNAwas isolated by gel electrophoresis and inserted into the appropriatesites of pBHA-1 by molecular cloning. The derived plasmid pGBC21-5 isillustrated in FIG. 31.

(b) Transformation of Bacillus

The “HpaII” Bacillus promoter was introduced upstream to the P₄₅₀C21cDNAgene by digestion with pGBC21-5 with the restriction enzyme Ndel,separation of the E. coli part of the shuttle plasmid by agarose gelelectrophoresis and subsequent religation and transformation of B.subtilis 1 A40 (BGSC 1 A40) competent cells. Neomycin resistant colonieswere analyzed to obtain pGBC21-6 (FIG. 32).

Transformation of the host B. licheniformis T5 (CBS 470.83) was alsoperformed with pGBC21-6. The plasmid remained stable in both Bacillushosts as revealed by restriction analysis.

EXAMPLE 19 Construction of a P₄₅₀C21cDNA Yeast Expression Vector andTransformation to the Yeast Host Kluyveromyces lactis

(a) Construction of the Expression Vector

To derive a suitable expression vector in yeast hosts for bovineP₄₅₀C21-2, pGBC21-2 was mutated by site directed mutagenesis asdescribed in Example 14. For the mutation, oligomer C21-6 (5′-CCT CTGCCT GGG TCG ACA AAA ATG GTC CTC GCA GGG-3′ (SEQ ID NO: 30)) was used tocreate a SalI restriction site and optimal yeast translation signalsupstream the ATG initiation codon as indicated in FIG. 33.

The SalI EcoRI DNA fragment of derived plasmid pGBC21-7 was ligated tothe 3′ P₄₅₀C21-EcoRI-fragment of pGBC21-1 and inserted by molecularcloning into the appropriate sites of pSP73 as indicated in FIG. 34.Derived pGBC21-8 was cut with SalI and EcoRV (EcoRV site was situated inthe multiple cloning site of pSP73) and the DNA fragment containing thefull-length P₄₅₀C21cDNA was inserted into the yeast expression vectorPGB950. Derived pGBC21-9 is depicted in FIG. 35.

(b) Transformation of K. lactis

15 μg of pGBC21-9 were digested with SacII and transformation of K.lactis CBS 2360 was performed as described in Example 5(c).

EXAMPLE 20 Molecular Cloning of a Full-length cDNA Encoding the BovineCytochrome P₄₅₀ Steroid 11β-Hydroxylase (P₄₅₀11β)

A bovine adrenal cortex cDNA library was prepared as described inExample 1 with one modification. An additional P₄₅₀11β-specific primer(oligomer 11β-1) with the nucleotide sequence 5′-GGC AGT GTG CTG ACACGA-3′ (SEQ ID NO: 32) was added to the reaction mixture of the firststrand cDNA synthesis oligomer 11β-1 was positioned just downstream tothe translation stop codon from position 1530 to 1513. Nucleotidesequences and map positions of mentioned P₄₅₀11β-oligomers were allderived from the P₄₅₀11βcDNA sequence data described by Morohasi et al.(J. Biochem., Vol. 102(3), pp. 559-568, 1987). The cDNA library wasscreened with a ³²P-labeled oligomer 11β-2 (5′-CCG CAC CCT GGC CTT TGCCCA CAG TGC CAT-3′ (SEQ ID NO: 33)) located at the 5′ end of theP₄₅₀11βcDNA from position 36 to 1.

Screening with oligomer 11β-2 revealed 6 hybridizing pfu's. These werefurther purified and analyzed with oligomer 11β-3 (5′-CAG CTC AAA GAGAGT CAT CAG CAA GGG GAA GGC TGT-3′, positions 990 to 955 (SEQ ID NO:34)). Two out of six showed a positive hybridizing signal with³²P-labeled oligomer 11β-3. The EcoRI inserts in both 11β-lambda-gt11recombinants were subcloned into the EcoRI-site of pTZ118R. One clonewith an EcoRI insert of 2.2 kb (pGB11β-1) was further analyzed byrestriction enzyme mapping and is shown in FIG. 36. pGB11β-1 containedall coding P₄₅₀11β cDNA sequences as determined by Morohashi et. al.

EXAMPLE 21 Construction of a P₄₅₀C21cDNA Bacillus Expression Vector andTransformation to the Bacterial Hosts Bacillus subtilis and Bacilluslicheniformis

(a) Construction of the Expression Vector

A full-length P₄₅₀11β cDNA with modified flanking sequences to theBacillus expression vector pBHA-1 was obtained by the PCR method(described in Example 18) with pGB11β-1 as template and two specificP₄₅₀11β-oligomers as primers.

Oligomer 11β-4 (5′-TTT GAT ATC GAA TTC CAT ATG GGC ACC AGA GGT GCT GCAGCC-3′ (SEQ ID NO: 35)) contained 21 bases complementary to the matureP₄₅₀11βcDNA sequence from position 72 to 93 and 21 bases to createEcoRV, EcoRI and NdeI restriction-sites and ATG initiation codon.Oligomer 11β-5 (5′-TAA CGA TAT CCT CGA GGG TAC CTA CTG GAT GGC CCG GAAGGT-3′ (SEQ ID NO: 36)) contained 21 bases complementary to the minusP₄₅₀11β cDNA strand upstream the translation stop codon at position 1511and 21 bases to create restriction-sites for EcoRV, XhoI and KpnI.

After PCR amplification with above mentioned template andP₄₅₀11β-primers, the amplified fragment (1.45 kb) was digested withEcoRI and KpnI and inserted by molecular cloning into the Bacillusexpression vector pBHA-1 cut with EcoRI and KpnI to obtain the vectorpGB11β-2 (see FIG. 36).

(b) Transformation of Bacillus

The “HpaIII” Bacillus promoter was introduced upstream to theP₄₅₀11βcDNA sequences by digestion of pGB11β-2 with NdeI, separation ofthe E. coli part of the shuttle plasmid by agarose gel electrophoresisand subsequent religation (as described in Example 18) andtransformation of B. subtilis 1A40 (BGSC 1A40) competent cells. Neomycinresistant colonies were analyzed and the plasmid, pGB11β-3, wasobtained. The derived plasmid pGB11β-3 was also transmitted to the B.licheniformis host strain T5 (CBS 470.83).

EXAMPLE 22 Construction of a P₄₅₀11βcDNA Yeast Expression Vector andTransformation to the Yeast Host Kluyveromyces lactis

(a) Construction of the Expression Cassette

A full-length P₄₅₀11β cDNA with modified flanking sequences to the yeastexpression vector pGB950 was obtained by the PCR method (described inExample 18) with pGB11β-1 as template and two specific P₄₅₀11β-oligomersas primers.

Oligomer 11β-6 (5′-CTT CAG TCG ACA AAA ATG GGC ACC AGA GGT GCT GCAGCC-3′ (SEQ ID NO: 37)) contained 21 bases complementary to the matureP₄₅₀11β cDNA sequence from position 72 to 93 and 18 additional bases tocreate a SalI restriction site, an optimal yeast translation signal andan ATG initiation codon. Oligomer 11β-5 is described in Example 21(a).After PCR amplification with the above mentioned template andP₄₅₀11β-primers, the amplified fragment (1.45 kb), was digested withSalI and XhoI and inserted by molecular cloning into the yeastexpression vector pGB950 cut with SalI to obtain the vector pGB11β-4(FIG. 37).

(b) Transformation of K. lactis

15 μg of pGB11β-4 were cut at the unique SacII site in the lactasepromoter and transformation of K. lactis CBS 2360 was performed asdescribed in Example 5(c).

EXAMPLE 23 Molecular Cloning of a Full-length cDNA Encoding the BovineAndrenodoxin (ADX), and Subsequent Transformation and Expression ofADXcDNA in the Yeast of Kluyveromyces lactis

(a) Molecular Cloning of ADX

A full-length ADXcDNA, with 5′ and 3′ flanking sequences modified to theyeast expression vector pGB950, was directly obtained from a bovineadrenal cortex mRNA/cDNA pool (for detailed description see Example 1)by amplification using the PCR method (see Example 18). For the ADXcDNAamplification, two synthetic oligomer primers were synthesized.

Oligomer ADX-1 (5′-CTT CAG TCG ACA AAA ATG AGC AGC TCA GAA GAT AAAATA-3′ (SEQ ID NO: 43)) contained 21 bases complementary to the 5′ endof the mature ADXcDNA sequence as described by Okamura et al (Proc.Natl. Acad. Sci. USA, Vol. 82, pp. 5705-5709, 1985) from positions 173to 194. The oligomer ADX-1 contained at the 5′ end 18 additionalnucleotides to create a SalI restriction site, an optimal yeasttranslation signal and an ATG initiation codon. The oligomer ADX-2(5′-TGT AAG GTA CCC GGG ATC CTT ATT CTA TCT TTG AGG ACT T-3′ (SEQ ID NO:44)) was complementary to the 3′ end of the minus strand of ADXcDNA fromposition 561 to 540 and contained additional nucleotides for creatingrestriction sites for BamHI, SmaI and KpnI.

The PCR was performed as described in Example 18 with 1 μM of eachADX-primers and 10 μl of mRNA/cDNA mixture (as described in Example 1)as template. A schematic view of this ADXcDNAa amplification is shown inFIG. 38.

The amplified fragment contained a full-length ADXcDNA sequence withmodified flankings, which was characterized by restriction-site analysisand nucleotide sequencing.

(b) Construction of the Expression Vector

The amplified ADX cDNA fragment was digested with SalI and SmaI andinserted by molecular cloning into the yeast expression vector pGB950cut with SalI and EcoRV. The derived plasmid pGBADX-1 is depicted inFIG. 38.

(c) Transformation of K. lactis

15 μg of pGBADX-1 were cut at the unique SacII-site in the lactasepromoter and transformation of K. lactis CBS 2360 was performed asdescribed in Example 5(c).

(d) Analysis of the Transformants

Two transformants, ADX-101 and ADX-102, and the control strain CBS 2360were selected for further analysis. The strains were grown inYEPD-medium for about 64 hours at 30° C. Total cellular protein wasisolated as described in Example 5(d). From the supernatants, 8 μlsamples were taken for analysis on immunoblots (see FIG. 39, lanes 3, 4and 5).

The results show that a protein of the expected length (14 kDa) wasexpressed in K. lactis cells transformed with pGBADX-1. The in vitroADX-activity of transformant ADX-102 is described in Example 24.

EXAMPLE 24 In vitro Activity of Adrenodoxin Obtained from Kluyveromyceslactis ADX-102

K. lactis ADX-102, obtained as described in Example 23, and controlstrain K. lactis CBS 2360 were grown in 100 ml of YEPD medium (1% yeastextract, 2% peptone, 2% glucose monohydrate) containing 2.5 ml of a 6.7%(w/w) yeast nitrogen base (Difco laboratories) solution and 100 mg 1⁻¹of geneticin (G418 sulfate; Gibco Ltd.), for 56 hours at 30° C. Thecells were collected by centrifugation (4,000×g, 15 minutes),resuspended in a physiological salt solution and washed with a phosphatebuffer (pH 7.0, 50 mM). After centrifugation (4,000×g, 15 minutes), thepellet was resuspended in a phosphate buffer (pH 7.0, 50 mM) resultingin a suspension containing 0.5 g cell wet weight/ml. The cells weredisrupted using a Braun MSK Homogenizer (6×15 seconds, 0.45-0.50 mmglass beads) and unbroken cells were removed by centrifugation (4,000×g,15 minutes). The cell-free extracts (40 mg protein/ml) were stored at−20° C.

ADX activity, i.e. electrotransfer capacity from adrenodoxin reductaseto cytochrome P₄₅₀SCC, in the cell-free extracts was determined by aP₄₅₀SCC activity assay. The assay mixture consisted of the followingsolutions:

Solution A (natural P₄₅₀SCC electron donating system with the exceptionof ADX): a 50 mM potassium phosphate buffer (pH 7.0) containing 3 mM ofEDTA, 2 μM of adrenodoxin reductase (purified from bovine adrenalcortex), 1 mM of NADPH (electron donor), 15 mM glucose-6-phosphate and16 units/ml of glucose-6-phosphate-dehydrogenase (NADPH regeneratingsystem).

Solution B (substrate and enzyme): a micellar solution of 75 μM ofcholesterol (doubly radiolabeled with [26,27-¹⁴C] cholesterol (40Ci/mol) and [7α-³H] cholesterol (400 Ci/mol)) and 1.5 μM of P₄₅₀ SCC(purified from bovine adrenal cortex) in 10% (v/v) Tergitol™ NP40/ethanol (1:1, v/v).

The assay was started by mixing 75 μl of solution A with 50 μl ofsolution B and 125 μl of cell-free extract or 125 μl of a potassiumphosphate buffer (50 mM, pH 7.0) containing 10 μM ADX (purified frombovine adrenal cortex). The mixture was stirred gently at 30° C. Sampleswere drawn after 15 minutes of incubation and diluted with 100 μl ofwater. From a sample, substrate and product(s) were extracted with 100μl of methanol and 150 μl of chloroform. After centrifugation (5,000×g,2 minutes), the chloroform layer was collected and dried. The dryresidue was dissolved in 50 μl of acetone containing 0.5 mg of a steroidmixture (cholesterol, pregnenolone and progesterone (1:1:1, w/w/w)) andsubsequently 110 μl of concentrated formic acid were added. Thesuspension was heated for 15 minutes at 120° C. and then, the ¹⁴C/³Hratio was determined by double label liquid scintillation counting. Theratio was a direct measure for the side chain cleavage reaction, becausethe ¹⁴C-labeled side chain was evaporated from the mixture asisocaprylic acid during the heating procedure.

Using this assay, ADX electron carrier activity could easily bedemonstrated in the cell-free extract of K. lactis ADX-102. In theassays with cell-free extract of K. lactis ADX-102 or with purified ADX,the side chain of the cholesterol was cleaved within 15 minutes in ayield of 50%, whereas in the assay with cell-free extract of the controlK. lactis CBS 2360, no side chain cleavage could be detected.

EXAMPLE 25 Molecular Cloning and Construction of a Full-length cDNAEncoding the Bovine Adrenodoxin Oxidoreductase (ADR), and SubsequentTransformation of ADRcDNA in the Yeast Kluyveromyces lactis

(a) Molecular Cloning of Adrenodoxin Oxidoreductase

A bovine adrenal cortex cDNA library was prepared as described inExample 1 with one modification. An additional ADR-specific primer(oligomer ADR-1) with the nucleotide sequence 5′-GGC TGG GAT CTA GGC-3′(SEQ ID NO: 49) was added to the reaction mixture of the first strandcDNA synthesis. Oligomer ADR-1 was located just downstream to thetranslation stop codon from position 1494 to 1480. Nucleotide sequencesand map positions of mentioned ADR-oligomers were all derived from theADRcDNA sequence data described by Nonaka et al, Biochem. Biophhys. Res.Comm., Vol. 145(3), pp. 1239-1247, 1987). The obtained cDNA library wasscreened with a ³²P-labeled oligomer ADR-2 (5′-CAC CAC ACA GAT CTG GGGGGT CTG CTC CTG TGG GGA-3′ (SEQ ID NO: 50)).

4 hybridizing pfu's were identified and subsequently purified. However,only 1 pfu showed also a positive signal with oligomer ADR-3 (5′-TTC CATCAG CCG CTT CCT CGG GCG AGC GGC CTC CCT-3′ (SEQ ID NO: 51)), which waslocated in the middle of the ADRcDNA (position 840 to 805). The ADRcDNAinsert (approx. 2 kb) was molecular cloned into the EcoRI-site ofpTZ18R. The obtained plasmid, pGBADR-1, contained a full-length ADRcDNAas revealed by restriction enzyme mapping and nucleotide sequencing. Thephysical map of pGBADR-1 is illustrated in FIG. 40.

(b) Construction of the Expression Cassette

A full-length ADR cDNA with modified flanking sequences to the yeastexpression vector, pGB950, was obtained by the PCR method (see Example18) with pGBADR-1 as template and two specific ADR-oligomers as primers.Oligomer ADR-4 ((5′-CGA GTG TCG ACA AAA ATG TCC ACA CAG GAG CAG ACC-3′(SEQ ID NO: 52)), contained 18 bases complementary to the mature ADRcDNAsequences from position 96 to 114 and 18 bases to introduce a SalIrestriction site, an optimal yeast translation signal, and an ATGinitiation codon.

Oligomer ADR-5 (5′-CGT GCT CGA GGT ACC TCA GTG CCC CAG CAG CCG CAG-3′(SEQ ID NO: 53)) contained 18 bases complementary to the minus strand ofADRcDNA upstream to the translation stop codon at position 1479 and 15bases to create KpnI and XhoI restriction sites for molecular cloning invarious expression vectors.

After amplification with the above mentioned template and ADR primers,the amplified fragment (1.4 kb) was digested with SalI and XhoI andinserted by molecular cloning into the yeast expression vector pGB950cut with SalI and XhoI. The derived plasmid, pGBADR-2, is illustrated inFIG. 40.

(c) Transformation of K. lactis

15 μg of pGBADR-2 was cut at the unique SacII-site in the lactasepromoter and transformation of K. lactis CBS 2360 was performed asdescribed in Example 5(c).

EXAMPLE 26 Molecular Cloning of a Full-length cDNA Encoding BovineNADPH-cytochrome P₄₅₀ Reductase (RED)

The bovine adrenal cortex cDNA library described in Example 1 wasscreened with a ³²P-labeled synthetic oligomer 5′-TGC CAG TTC GTA GAGCAC ATT GGT GCG TGG CGG GTT AGT GAT GTC CAG GT-3′ (SEQ ID NO: 54),specific for a conserved amino acid region within rat-, porcine- andrabbit RED as described by Katagari et al (J. Biochem., Vol. 100, pp.945-954, 1986) and Murakami et al. (DNA, Vol. 5, pp. 1-10, 1986).

Five hybridizing pfu's were obtained and further characterized byrestriction enzyme mapping and nucleotide sequencing. A full-lengthREDcDNA was inserted into expression vectors and transformed toappropriate hosts as mentioned in Examples 2, 3 and 6.

EXAMPLE 27 Construction, Transformation and Expression of an ExpressionCassette Encoding the Proteins P₄₅₀SCC and ADX in the YeastKluyveromyces lactis

(a) Construction of the Expression Cassette

The expression cassette pGBADX-1 (see Example 23) was digested withSacII and HindIII (partially) and sticky ends were filled in usingKlenow DNA polymerase. The DNA fragment comprising a part of the lactasepromoter (but still functional), the coding ADX sequence and the lactaseterminator was separated and isolated by agarose-gel electrophoresis andsubsequently inserted into pGBSCC-7, which was first linearized by XbaIdigestion (see Example 5(b)) and sticky ends filled in using Klenow DNApolymerase. The construction was set up so that a unique restrictionsite (SacII) was obtained, which is necessary to transfer the plasmid toK. lactis.

This unique SacII restriction site was located in the lactase promotersequence flanking the SCC sequence, as the SacII restriction site in thelactase promoter flanking the ADX sequence was destroyed by the fill-inreaction. The obtained expression cassette pGBSCC ADX-1 contained thecoding sequence for SCC as well as for ADX, each driven by the lactasepromoter.

(b) Transformation of K. lactis

Transformation of K. lactis CBS 2360 was performed as described inExample 5(c) with 15 μg of pGBSCC/ADX-1, linearized at the unique SacIIrestriction site. One transformant (SCC/ADX-101) was selected from SCCand ADX expression studies.

(c) Analysis of the Transformant K. lactis SCC/ADX-101

Cellular protein fractions were prepared from cultures of theSCC/ADX-101 and the control strain CBS 2360 as described in Example 5(d)and analyzed by SDS/PAGE and Western-blotting. The blot was probed withantibodies specific for SCC and ADX, respectively. Compared to thecontrol strain, the cellular protein fraction of transformantSCC/ADX-101 showed two additional bands of expected length (53 and 14kDa, respectively) showing the expression of both proteins SCC and ADX.Expression levels of both in transformant SCC/ADX-101 were comparablewith levels observed in transformants expressing only one protein (forSCC see FIG. 15A, lane 3, and for ADX FIG. 39, lane 5). The in vitro SCCand ADX activity of transformant SCC/ADX-101 is described in Example 28.

EXAMPLE 28 In vitro Activity of P₄₅₀SCC and Adrenodoxin Obtained FromKluyveromyces lactis SCC/ADX-101

K. lactis SCC/ADX-101 obtained as described in Example 27 and controlstrain K. lactis SCC-101 as described in Example 5(d) were grown in 1liter of YEPD medium (1% yeast extract, 2% peptone, 2% glucosemonohydrate) containing 100 mg 1⁻¹ of geneticin (G418 sulfate; GibcoLtd.), for 72 hours at 30° C. The cells were collected by centrifugation(4,000×g, 15 minutes), resuspended in a physiological salt solution andwashed with a phosphate buffer (pH 7.5, 75 mM). After centrifugation(4,000×g, 15 minutes), the pellet was resuspended in a phosphate buffer(pH 7.5, 75 mM) resulting in a suspension containing 0.5 g cell wetweight/ml. The cells were disrupted using a Braun MSK Homogenizer (6×15seconds, 0.45-0.50 mm glass beads). Unbroken cells were removed bycentrifugation (4,000×g, 15 minutes).

In the cell-free extracts, the activity of the protein complexP₄₅₀SCC/ADX was assayed by determining the cholesterol side-chaincleaving reaction in the presence of NADPH and ADR. The assay mixtureconsisted of the following solutions:

Solution A (natural P₄₅₀SCC electron donating system with the exceptionof ADX): a 50 mM potassium phosphate buffer (pH 7.0) containing 3 mM ofEDTA, 2 μM of adrenodoxin reductase (purified from bovine adrenalcortex), 1 mM of NADPH (electron donor) 15 mM of glucose-6-phosphate and16 units/ml of glucose-6-phosphate-dehydrogenase (NADPH regeneratingsystem).

Solution B (substrate and enzyme): a micellar solution of 37.5 μM ofcholesterol (doubly radiolabeled with [26,27-¹⁴C] cholesterol (40Ci/mol) and [7α-³H] cholesterol (400 Ci/mol)) in 10% (v/v) Tergitol™ NP40/ethanol (1:1, v/v).

The assay was started by mixing 75 μl of solution A with 50 μl ofsolution B and 125 μl of cell-free extract. The mixture was stirredgently at 30° C. Samples were drawn after 60 minutes of incubation anddiluted with 100 μl of water. From a sample, substrate and products(s)were extracted with 100 μl of methanol and 150 μl of chloroform. Aftercentrifugation (5,000×g, 2 minutes), the chloroform layer was collectedand dried. The dry residue was dissolved in 50 μl of acetone containing0.5 mg of a steroid mixture (cholesterol, pregnenolone and progesterone(1:1:1, w/w/w)) and subsequently 110 μl of concentrated formic acid wereadded. The suspension was heated for 15 minutes at 120° C. Then, the¹⁴C/³H ratio was determined by double label liquid scintillationcounting. The ratio was a direct measure for the side-chain cleavagereaction, because the ¹⁴C-labeled side chain was evaporated from themixture as isocaprylic acid during the heating procedure.

Using this assay, cholesterol side-chain cleaving activity wasdemonstrated in the cell-free extract of K. lactis SCC/ADX-101, whereasthe cell-free extract of K. lactis SCC-101, no activity was detectable.By means of HPLC-analysis, the reaction product produced by a cell-freeextract of K. lactis SCC/ADX-101 was identified as pregnenolone.

EXAMPLE 29 Construction and Transformation of an Expression CassetteEncoding Bovine Cytochrome P₄₅₀ Steroid 17α-Hydroxylase and BovineCytochrome P₄₅₀ Steroid C21-Hydroxylase in the Yeast Kluyveromyceslactis

(a) Construction of the Expression Cassette

The expression cassette pGB17α-5 (FIG. 41) described in Example 14, wasdigested with SacII and HindIII (partially) and sticky ends were filledin using Klenow DNA polymerase. The DNA fragment comprising a part ofthe lactase promoter, the sequence coding for P₄₅₀17α and the lactaseterminator were separated and isolated by agarose gel electrophoresisand subsequently inserted into pGBC21-9 (FIG. 42) described in Example19, which was first linearized by XbaI digestion and sticky ends filledin using Klenow DNA polymerase. The obtained expression cassette,pGB17α/C21-1 (FIG. 43), had a unique SacII restriction site because theSacII restriction site in the lactase promotor flanking the P₄₅₀17αsequence was destroyed by the fill-in reaction.

(b) Transformation of K. lactis

Transformation of K. lactis CBS 2360 was performed as described inExample 5(c) with 15 μg of pGB17α/C21-1, linearized at the unique SacIIrestriction site. One transformant 17α/C21-101 was further analyzed forin vivo activity of both, P₄₅₀17α and P₄₅₀C21 (see Examples 30 and 31).

EXAMPLE 30 In vitro Activity of P₄₅₀17α and P₄₅₀C21 Obtained fromKluyveromyces lactis 17α/C21-101

K. lactis 17α/C21-101 obtained as described in Example 29, K. lactis17α-101 as described in Example 14 and K. lactis CBS 2360 were grown in100 ml of medium D. Medium D contained per liter of distilled water:

Yeast extract (Difco) 10 g Bacto Peptone (Oxoid) 20 g Dextrose 20 g pH =6.5

After sterilization and cooling to 30° C., 25 mg of geneticin (G418sulfate; Gibco Ltd.) dissolved in 1 ml of distilled water sterilized bymembrane filtration was added. The cultures were grown for 72 hours at30° C. and the cells were collected by centrifugation (4,000×g, 15minutes). The pellet was washed with phosphate buffer (50 mM, pH=7.0)and cells were collected by centrifugation (4,000×g, 15 minutes). Thepellet was taken up in phosphate buffer (50 mM, pH=7.0) resulting in asuspension containing 0.5 g wet weight/ml. This suspension was disruptedby sonification (Braun labsonic 1510; 12×1 minute, 50 Watts). Unbrokencells were removed by centrifugation (12,000×g, 15 minutes).

Cell-free extracts were assayed for P₄₅₀17α activity and P₄₅₀C21activity by determining the production of 17α,21 dihydroxyprogesteronein the presence of NADPH. The assay mixture consisted of the followingsolutions:

Solution A: a 50 mM potassium phosphate buffer (pH=7.0), containing 3 mMof EDTA, 2 mM of NADPH, 50 mM of glucose-6-phosphate and 16 units/ml ofglucose-6-phosphate-dehydrogenase (NADPH-regenerating system).

Solution B (substrate): a micellar solution of 80 μM of [4-¹⁴c]progesterone (30 Ci/mol) in 10% (v/v) Tergitol™ NP 40/ethanol (1:1, v/v)in a potassium phosphate buffer (75 mM, pH=7,5).

The assay was started by mixing 75 μl of Solution A with 50 μl ofSolution B and 125 μl of cell-free extract. The mixture was stirredgently at 30° C. and 50 μl samples were drawn after 60 minutes ofincubation and added to a mixture of 100 μl of methanol and 50 μl ofchloroform. Subsequently, 100 μl of chloroform and 100 μl of water wereadded. The chloroform layer was collected by centrifugation (5,000×g, 2minutes) and the water/methanol layer was re-extracted with 100 μl ofchloroform. The two chloroform layers were combined and dried. The dryresidue was dissolved in 100 μl of acetonitrile/H₂O (9:1, v/v) and 50 μlsamples were eluted with acetonitrile/H₂O (58:42, v/v) using an HPLCcolumn (Chrompack lichr. 10RP18, 250×4.6 mm). In the eluate, the steroidsubstrate and products were detected by a flow scintillation counter anda U.V. detector. The radioactivity of the collected fractions wasdetermined by liquid scintillation counting. Using the assay, it wasfound that a cell-free extract obtained from K. lactis 17α/C21-101produced 17α,21 dihydroxy progesterone, whereas cell-free extractsobtained from K. lactis 17α-101 and K. lactis CBS 2360 did not. The mainproduct produced by K. lactis 17α-101 appeared to be 17α hydroxyprogesterone.

EXAMPLE 31 In vivo Activity of P₄₅₀17α and P₄₅₀C21 in Kluyveromyceslactis 17α/C21-101

K. lactis 17α/C21-101 obtained as described in Example 29 and K. lactisCBS 2360 were inoculated in 25 ml of medium D. Medium D contained perliter of distilled water:

Yeast extract (Difco) 10 g Bacto Peptone (Oxoid) 20 g Dextrose 20 g pH =6.5

After sterilization and cooling to 30° C., 25 mg of geneticin dissolvedin 1 ml of distilled water sterilized by membrane-filtration was addedto 1 liter of medium D. Then, 100 μl of a solution containing thesubstrate [4-¹⁴C] progesterone were added to 25 ml of the completedmedium. The substrate solution contained 800 μl [4-¹⁴C] progesterone (8Ci/mole) per ml in 10% (v/v) Tergitol™ NP 40/ethanol (1:1, v/v). Thecultures were grown at 30° C. in a rotary shaker (240 rpm) and samplesof 2 ml taken after 0 and 68 hours were drawn. Each sample was mixedwith 2 ml of methanol. After 24 hours of extraction at 4° C., themixtures were centrifugated (4,000×g, 15 minutes). From the obtainedsupernatant, samples of 200 μl were eluted with acetonitrile/H₂O (58:42,v/v) using an HPLC column (Chrompack Lichr. 10 RP18, 250×4.6 mm).

In the eluate, the steroid substrate and products were detected. Theradioactivity of the collected fractions was determined by liquidscintillation counting. One of the fractions obtained from a culture ofK. lactis 17α/C21-101 grown for 68 hours clearly showed the presence of17α,21 dihydroxyprogesterone, whereas this compound was not produced ina culture of the control strain K. lactis CBS2360.

EXAMPLE 32 Construction Transformation and Expression of an ExpressionCassette Encoding the Human 3β-HSDH in the Yeast SaccharomycesCerevisiae

1. Generation of pUC derivatives with new polylinker sites.

M13mp19 (Yanisch-Peron, C. et al., Gene 33 (1985) p 103-119) wasmutagenized using oligonucleotide

OTG2805: 5′ GCGCTCAGCGGCCGCTTTCCAGTCG 3′ (SEQ ID NO: 59)

and a NotI site was introduced into the remaining sequence of the lacIgene (M13TG724). Then, a polylinker containing EcoRI, SnaBI and NotIsites was introduced in the EcoRI site of M13TG724 usingoligonucleotides

OTG2793: 5′ AATTGCGGCCGCGTACGTATG 3′ (SEQ ID NO: 60) and

OTG2796: 5′ AATTCATACGTACGCGGCCGC 3′ (SEQ ID NO: 61)

However, during the cloning step, multiplication and modification of theinsert occurred. The resulting M13TG7244 had the following sequence:

GAATTCATACGTACGCGGCCGCAATTGCGGCCGGTACGTATAATTCACTGGCCGT (SEQ ID NO: 62)

Note that the EcoRI, SnaBI and NotI sites are underlined and that thelacZ sequence of pUC19 is in italics. M13TG7244 was digested with EcoRIand SstI restriction enzymes and a linker was introduced usingoligonucleotides

OTG2919: 5′ CAACGCGTCCTAGG 3′ (SEQ ID NO: 63) and

OTG2920: 5′ AATTCCTAGGACGCGTTGAGCT 3′ (SEQ ID NO: 64)

yielding M13TG7246. This linker added MluI and AvrII sites. A PvuIIfragment containing the relevant restriction sites of M13TG7246 wassubcloned into pUC19, yielding pTG7457 (FIG. 44).

pUC19 (Yanisch-Peron, C. et al., Gene 33 (1985) p 103-119) was digestedwith BamHI and EcoRI restriction enzymes and a polylinker was introducedusing oligonucleotides

OTG2792: 5′ GATCCGCAGATATCATCTAGATCCCGGGTAGAT 3′ (SEQ ID NO: 65),

OTG2797: 5′ AGAGCTCAAGATCTACCCGGGATCTAGATGATATCTGCG 3′ (SEQ ID NO: 66),

OTG2794: 5′ CTTGAGCTCTACGCAGCTGGTCGACACCTAGGAG 3′ (SEQ ID NO: 67) and

OTG2795: 5′ AATTCTCCTAGGTGTCGACCAGCTGCGT 3′ (SEQ ID NO: 68)

yielding pTG7453 (FIG. 45).

Subcloning of the Terminator.

PGK Terminator:

The polylinker sites between BamHI and SstI of pTG7453 were introducedinto a pTG7457 derivative and the new plasmid was digested with BglIIand HindIII restriction enzymes and a similarly restricted fragmentcontaining the PGK terminator (Hitzeman, R. A. et al., Nucleic AcidsRes. 10 (1982) 7791-7808); Loison, G. et al., Yeast 5 (1989) p 497-507)was cloned into it. The new plasmid was termed pTG10014 (FIG. 46).pTG10014 was digested with ClaI restriction enzyme and the cohesive endsfilled in with the Klenow polymerase yielding pTG10015.

Subcloning of the Promoters.

a) The CYC1 Promoter:

The polylinker sites between BamHI and SstI of pTG7453 were introducedinto a pTG7457 derivative and the new plasmid was opened by SnaBIrestriction enzyme and the RsaI DraI fragment of 456 nucleotides ofpEMBL8 (Dente et al., Nucleic Acids Res. 11 (1983) p 1645-1655),containing the origin of replication of phage f1, was introducedgenerating pTG7503. A 0.78 kb BamHI HindIII fragment of pGBSCC-9,prepared in Example 6 containing the CYC1 promoter of Saccharomycescerevisiae, a polylinker and the lactase terminator of Kluyveromyceslactis, were subcloned in pTG7503, yielding pTG10004 (FIG. 47). The XhoIand MluI sites of the CYC1 promoter were eliminated by site directedmutagenesis using oligonucleotide

OTG4410: 5′ GCGGATCTGCTCGAAGATTGCCTGCGCGTTGGGCTTGATC 3′ (SEQ ID NO: 69)

on ssDNA of pTG10004. This yielded pTG10005. pTG10005 was digested withSalI and XhoI restriction enzymes and a MluI site was introduced usingoligonucleotides

OTG4433: 5′ TCGACGGACGCGTGG 3′ (SEQ ID NO: 70) and

OTG4434: 5′ TCGACCACGCGTCC 3′ (SEQ ID NO: 71)

yielding pTG10006.

b) The GAL10/CYC1 Promoter:

The pYeDP1/8-2 (Cullin, C., Gene 65 (1988) p 203-217) plasmid was openedwith XhoI restriction enzyme. The cohesive ends were filled in withklenow polymerase and the plasmid was religated. In pTG10010, theGAL10/CYC1 promoter no longer contained the XhoI site and this served asa template for a PCR amplification.

2. Construction of the Expression Vectors.

In pTG7503, part of the remaining lacZ coding sequence was eliminated bysite directed mutagenesis using oligonucleotide

OTG4431: 5′ TGGCCGTCGTTTTACTCCTGCGCCTGATGCGGTAT 3′ (SEQ ID NO: 72)

yielding pTG7549. The LacZ promoter present in pTG7549 was deleted usingoligonucleotides

OTG4470: 5′ GGCCGCAAAACCAAA 3′ (SEQ ID NO: 73) and

OTG4471: 5′ AGCTTTTGGTTTTGC 3′ (SEQ ID NO: 74)

which were inserted after a NotI HindIII restriction, restoring bothsites. The new construct was termed pTG7553. A BamHI MluI fragmentcontaining the CYC1 promoter of pTG10006 and the MluI HindIII fragmentcontaining the PGK terminator of pTG10015 were ligated together. Theligation material was then added to pTG7553, previously digested withMluI and HindIII restriction enzymes. Finally, oligonucleotide

OTG4478: 5′ GATCTATCGATGCGGCCGCG 3′ (SEQ ID NO: 75)

hybridized with oligonucleotide

OTG4479: 5′ CGCGCGCGGCCGCATCGATA 3′ (SEQ ID NO: 76)

(BamHI MluI linkers containing ClaI NotI sites) was added, and ligatedtogether. The resulting plasmid was termed pTG10031 (FIG. 48). The PCRamplified fragment obtained with pYeDP1/8-2 was digested with ClaI andSalI restriction enzymes and introduced into pTG10031 digested with thesame enzymes yielding pTG10033 (FIG. 49).

3. Construction of the Basic Vector

pTG3828 (Achstetter, T. et al., Gene 110 (1992) p 25-31) was digestedwith BglII and BamHI restriction enzymes and a polylinker segment ofpPOLYIII (Lathe R. et al., Gene 57 (1987) p 193-201) covering the BglIIBamHI sites was introduced. The orientation which had lost the BglII andBamHI sites was chosen (pTG10012). pTG10012 was digested with NotI andEcoRI restriction enzymes and ligated to the large EcoRI NotI fragmentof pTG7549 and this generated pTG10013 (FIG. 50). The URA3-D fragment onthis plasmid was bordered by HindIII sites.

4. Construction of the Recombination Vectors.

The NotI cassettes containing the CYC1 or the GAL10/CYC1 promoter andthe PGK terminator were subcloned into vectors containing the URA3-dgene in both orientations, yielding recombination vectorspTG10041-pTG10042 and pTG10045-pTG10046 respectively. pTG10013 wasdigested with NotI restriction enzyme and the NotI fragments containingthe expression block of pTG10031 were ligated into it yielding twoorientations, pTG10041 (FIG. 51) and pTG10042 (FIG. 52). Similarly,pTG10045 (FIG. 53) and pTG10046 (FIG. 54) were obtained from pTG10033and pTG10013.

5. Construction of Transfer Vectors

The cDNA coding for human 3βHSDH Type I, obtained from Labrie, wascontained in the EcoRI site of pT7T3 vector. The coding sequencecorresponded to the sequence published previously by V. Luu The et al.(1989) Mol. Endocrinol. Vol. 3, pp. 1310-1312, except that the 5′contained an additional GGG. This plasmid was modified to allow directcloning in the expression vectors. First, a linker containing a MluIsite using oligonucleotide

OTG4539 : 5′ AATTGGACGCGTCC 3′ (SEQ ID NO: 77)

was introduced at the 3′ end of the coding sequence after partial EcoRIdigestion (pTG10036). The EcoRI site of pTG10036 was treated by MungBean Nuclease and the resultant DNA was digested by MluI restrictionenzyme. On the other hand, a SalI MluI insert of 1.7 kb was cloned intothe SalI MluI sites of pTG10031 (pTG10058). The SalI site of pTG10058which carried the CYC1 promoter was filled in with Klenow polymerase andthe resultant plasmid was digested with MluI restriction enzyme.Ligation of these fragments yielded pTG10064 (FIG. 55) which containedthe coding sequence for 3βHSDH bordered by SalI and MluI restrictionsites. The SalI MluI fragment from pTG10064 was subcloned into pTG10033yielding pTG10065 (FIG. 56) with 3βHSDH under control of GAL10/CYC1.

6. Expression of 3βHSDH in S. cerevisiae

The yeast used in this study was strain W303-1B (MATα, ρ⁺, ura3-1,leu2-3, -112, his3-11, -15, trpl-1, ade2-1, can^(R) (?), cyr⁺(?)[Crivellone et al., J. Biol. Chem. 263 (1988) 14323-14333) as a modelstrain. W303-1B was auxotrophic for uracil, leucine, histidine,tryptophane, adenine and resistant to canavanine.

a) Construction of a Yeast—E. coli Shuttle Vector for the Expression of3βHSDH.

Using the recombination vectors, assembly of the desired expressionplasmid via recombination in vivo can be accomplished. Yeast was madeelectrocompetent and was transformed using 100 ng of pTG10042(restricted with SalI and MluI) and pTG10065 (restricted with NotI).After electroporation, the cells were plated on selective YNBG mediumcontaining adenine, tryptophane, leucine and histidine but no uracil.After 3-4 days of growth, colonies were purified on the same medium.Saccharomyces cerevisiae recombined expression plasmid (SCREP) pTG10201(PromCYC1-3β HSDH-PGKterm) was obtained in strain (W303-1B). The latterSCREP was obtained by an in vivo recombination between the GAL10/CYC1promoter and the CYC1 promoter, reconstructing the CYC1 promoter.

b) Detection of 3β HSDH Antigen in Yeast by Western Blotting.

Antibodies

The rabbit anti-3β HSDH antibodies against human 3βHSDH were obtainedfrom F. Labrie and have been described in V. Luu The et al., (1989) Mol.Endocrinol. Vol. 3, pp. 1310-1312.

Western Blotting

Western blotting was done as described previously (E. Degryse et al.,(1992) Gene Vol. 118, pp. 47-53) except that anti-3βHSDH antibodies wereused.

c) Compartmentation.

Compartmentation was studied in strain W303-1B transformed with SCREPpTG10201 (CYC1+3β HSDH). Cells were divided into cytosol, mitochondriaand microsomes according to C. Cullin and al., Gene 65 (1988) p 203-217.Western blots and activity measurements were performed on fractions ofthe untransformed and two transformed strains. The control(untransformed strain) was found to be negative all over. For the otherstrains, most of the activity was found in the mitochondrial andmicrosomal fractions. These results were confirmed in the Western blot,showing the correct size of the expressed gene product.

d) In vitro Activity of 3β HSDH After Induction in Minimal Medium andCell Fractionation.

Cells were grown until an optical density between 2 and 5 at 600 nm, inYNBG medium supplemented with casamino acids (0,5%) and tryptophane,adenine, histidine and leucine. After harvest of the cells bycentrifugation, microsomes were prepared according to C. Cullin and al.,Gene 65 (1988) p 203-217. The 3β HSDH activity was measured with themethod of Bauer H. C. et al., J. Steroid Biochem. 33 (1989) 643-646. Themicrosomes were taken up in TrisHCl 50 mM pH7.4, EDTA 2 mM, glycerol 20%and stored at −20° C. until used. The protein concentration was 3.75mg/ml. Activity was measured in DPBS+BSA (0.175 ml)+pregnenolone (0.005ml;1 μCi=40 nmole/ml) and 19 μg of microsomal extract/tube. The reactionwas started by the addition of NAD 10 mM (0.015 μl) and lasted for 60minutes at 37° C. Controls were used in which the reaction was stoppedimmediately after substrate addition to the complete reaction mixture(t=0h) or to the NAD deleted reaction mixture (t=0h−NAD).

The in vitro activity of 3β HSDH was measured using radioactivepregnenolone. After incubation at 37° C., the bulk of the pregnenolonewas precipitated with digitonin and the soluble product (progesterone)was measured by scintillation counting. A microsomal fraction ofW303-1B/pTG10201 (CYC1+3β HSDH) was shown to be active in the presenceof NAD only.

NAD dependence of 3β HSDH activity t = 0h − (t = 0h − NAD) 60′ − (t = 0h− NAD) + NAD 17 000 463 000 − NAD    0     0

Activity was also measured after cell fractionation (see above).Activity was measured in DPBS+BSA (0.077 ml)+pregnenolone (0.002 ml;1μCi=40 nmole/ml)+NAD (0.010 μl, 10 mM) and 7 μg of cytosolic extract, 9μg of mitochondrial extract and 6 μg of microsomal extract/tube.

W303 net CPM/15′/μg cytosol 312 mitochondria 297 microsomes 178W303/pTG1020 (Prom CYC1 3β HSDH PGK 1 term) Percentage cytosol  65779.7% mitochondria 42308 62.7% microsomes 18590 27.5%

The activity measurements coincided with the results of the Westernblot. Activity was found in the mitochondrial and microsomal fraction.No activity was present in the cytosol nor in any fraction obtained fromuntransformed yeast. After a 15 minutes incubation at 37° C., theconversion of pregnenolone (0.8 μM) into progesterone was measured for 1μg amounts of the following fractions: mitochondria, 60% conversion;micro-somes, 15% conversion, cytosol, 3% conversion. The reaction wasnot linear with time, but this point was not investigated further. Theconversion of pregnenolone into progesterone was demonstrated in vivo(see below).

e) In vivo Activity of 3β HSDH

Bioconversion of pregnenolone into progesterone:

Transformed yeast cells were grown in the presence of 100 μg/ml ofpregnenolone and samples were extracted and analyzed by RP-HPLC forconversion into progesterone. The preliminary results showed theaccumulation of progesterone in the culture medium of transformed yeast.15% of pregnenolone was converted into progesterone in 2 days.

EXAMPLE 33 Construction, Transformation and Bioconversion from anExpression Cassette Encoding Human 3β-HSDH and Bovine P₄₅₀ 17α inSaccharomyces cerevisiae 1. Construction of Transfer Vectors for Human3β-HSDH and Bovine P₄₅₀ 17α

a) Sub-cloning of the cDNA coding for the bovine P₄₅₀ 17α:

The cDNA coding for the bovine P₄₅₀ in plasmid. pGB17α-5 described inexample 14 (FIG. 24) was reformatted on SalI MluI restriction sites byintroduction of a MluI site into the XhoI site of the vector. The SalIMluI fragment was subcloned into pTG10031 (example 32, FIG. 48) undercontrol of the CYC1 promoter. This vector was called pTG10058.

b) Sub-cloning of the human 3β-HSDH type I:

The vector pTG 10065 with cDNA encoding human 3β-HSDH type I undercontrol of the Gal10/CYC1 promoter was obtained in Example 32 (FIG. 56).

2. Construction of a Yeast-E. coli Shuttle Vector for the Expression ofHuman 3βHSDH Type I and Bovine P₄₅₀17α

Using recombination vectors, assembly of the desired expression plasmidvia recombination in vivo can be accomplished. Plasmids containingCYC1_(prom)-PGK_(term) and the cDNAs for bovine P₄₅₀ 17α or human3β-HSDH type I were coupled with LEU2 or URA3-d as selection markers,respectively. Recombination vectors were generated containing the yeast2 μm, a replicon, an expression cassette with the CYC1_(prom)-PGK_(term) and different selection markers URA3-d (pTG10259) orLEU2 (pTG10260). pTG10259 is identical to the previously describedrecombination vector pTG10042 previously described in Example 32 (FIG.52) except that the single XbaI site contained in the 2 μm region wasreplaced by a XbaI site, obtained through filling in by the Klenowpolymerase and religation.

The LEU2 containing recombination vector was constructed as follows.Into a plasmid containing the LEU2 gene (Genbank locus YSCLEU2,accession number JO1333), HindIII sites into the HpaI site (located atposition 241 were introduced in YSCLEU2, using as an adaptoroligonucleotide OTG4464: CACAAGCTTGTG (SEQ ID NO: 78)) and SalI site (atposition 2213 in YSCLEU2, using as an adaptor oligonucleotide OTG4463:TCGAGGGAAGCT (SEQ ID NO: 79)). The HindIII fragment was cloned intopTG10013 (see FIG. 50) digested with HindIII restriction enzyme and wastreated with phosphatase. This yielded both orientations, pTG10023 andpTG10024.A NotI fragment containing the expression block of pTG10031(FIG. 48) was subcloned into pTG10023 and yielded pTG10158. Theorientation of the selection marker and the expression block in pTG10158was similar to that present in pTG10042 (FIG. 52). pTG10158 generatedpTG10260 simply by eliminating the single XbaI site contained in the 2μm region, as done above. The expression blocks from pTG10065 (human3β-HSDH type I) and pTG10058 (bovine P₄₅₀ 17α) were introduced next,yielding the final expression plasmids, respectively pTG10261 andpTG10269.

3. Transformation of Saccharomyces cerevisiae

Yeast strain W303-1B was transformed using a transformation protocoldescribed by Lauermann, Curr. Genetics, Vol. 20, pp. 1-3, (1991).Ethanol improved the transformation efficiency of intact yeast cells.The yeast cells were transformed with 1 μg of pTG10261 +pTG10269 (nocarrier DNA was utilized). After transformation and plating out on agarplates containing YNBG+casamino acids 0.01%+WAH or YNBG casamino acids0.01%+WAHL, candidate colonies were confirmed on selective medium.Selection was done on YNBG+casamino acids 0.01%+WAH(W=Trp,A=adenine,H=His). PCR was used to confirm the simultaneouspresence of the selective marker and the cDNA associated with it.

4. In vivo Activity of P₄₅₀ 17α and 3β-HSDH in Saccharomyces cerevisiae

Bioconversion was measured with 100 μg/ml of pregnenolone incubated at30° C. with cells on YNB+glycerol+WAH medium. Samples were taken after 2days, then were extracted and analyzed by RP-HPLC. Values for17α-hydroxyprogesterone (17OH-PROG) and progesterone (PROG) wereexpressed as μg/ml with duplicate data from different clones. Thefollowing results were obtained.

Product Product W303-1B PROG 170H-PROG PROG 170H-PROG pTG10261 +pTG10269 1.6 3.2 0.6 4.6

The bioconversion of pregnenolone into 17α-hydroxyprogesterone wasachieved in yeast by coexpression of 3β-HSDH and P₄₅₀ 17α.

EXAMPLE 34 In vivo Activity of Bovine P₄₅₀17α in TransformedKluyveromyces lactis

Transformation of K. lactis strain CBS 2360 was performed with pGB 17α-5as described in Example 14 and in vivo activity was determined in thewhole cells of the transformed K. lactis strain. Four independenttransformants (17α-3,17α-7,17α-10 and 17α-11) were grown in rich medium(10 g of yeast extracts, 10 g of bactopeptone and 20 g of glucose/liter)for 72 hours to reach an A600 of at least 30. The cells were harvestedand resuspended at 1×10⁶ cells/ml (A600 =1).

Five ml of culture were incubated in the presence of ³H-labelledprogesterone (20 μM) for 24 hours at 28° C. and then were extracted withdichloromethane. RP-HPLC analysis showed that progesterone wasspecifically transformed into 17α-hydroxyprogesterone. The amount of17α-hydroxyprogesterone was about 40% (about 23% to 58% depending on thetransformant) of the substract added (see FIG. 57 corresponding to17α-3). No androstenedione, which was the product of the C17-20-lyaseactivity of P₄₅₀17α, was detected.

³H-labelled 17α-hydroxyprogesterone was also incubated with thetransformants under the conditions described above and after 24 hours ofincubation, no androstenedione was detected. These data indicate thatthe bovine P₄₅₀17α expressed in K. lactis under the lactase promoterdoes not show any activity C17-20 lyase.

Various modifications of the products and method of the invention may bemade without departing from the spirit or scope thereof and it is to beunderstood that the invention is intended to be limited only as definedin the appended claims.

79 37 NUCLEIC ACID SINGLE LINEAR OLIGOMER SSC-1 1 GGCTGACGAA GTCCTGAGACACTGGATTCA GCACTGG 37 177 NUCLEIC ACID DOUBLE LINEAR SYNTHETICPSTI/HINDIII FRAGMENT 2 TGCAGCAGCG GCGGCAATCA GTACTAAGAC CCCTAGGCCTTACAGTGAGA TCCCCTCCCC 60 TGGTGACAAT GGCTGGCTTA ACCTCTACCA TTTCTGGAGGGAGAAGGGCT CACAGAGAAT 120 CCACTTTCGC CACATCGAGA ACTTCCAGAA GTATGGCCCCATTTACAGGG AGAAGCT 177 7336 NUCLEIC ACID DOUBLE UNKNOWN PLASMID pBHA-1 3AATTCACCTC GAAAGCAAGC TGATAAACCG ATACAATTAA AGGCTCCTTT TGGAGCCTTT 60TTTTTTGGAG ATTTTCAACG TGAAAAAATT ATTATTCGCA ATTCCAAGCT AATTCACCTC 120GAAAGCAAGC TGATAAACCG ATACAATTAA AGGCTCCTTT TGGAGCCTTT TTTTTTGGAG 180ATTTTCAACG TGAAAAAATT ATTATTCGCA ATTCCAAGCT CTGCCTCGCG CGTTTCGGTG 240ATGACGGTGA AAACCTCTGA CACATGCAGC TCCCGGAGAC GGTCACAGCT TGTCTGTAAG 300CGGATGCAGA TCACGCGCCC TGTAGCGGCG CATTAAGCGC GGCGGGTGTG GTGGTTACGC 360GCAGCGTGAC CGCTACACTT GCCAGCGCCC TAGCGCCCGC TCCTTTCGCT TTCTTCCCTT 420CCTTTCTCGC CACGTTCGCC GGCTTTCCCC GTCAAGCTCT AAATCGGGGG CTCCCTTTAG 480GGTTCCGATT TAGTGCTTTA CGGCACCTCG ACCCCAAAAA ACTTGATTAG GGTGATGGTT 540CACGTAGTGG GCCATCGCCC TGATAGACGG TTTTTCGCCC TTTGACGTTG GAGTCCACGT 600TCTTTAATAG TGGACTCTTG TTCCAAACTG GAACAACACT CAACCCTATC TCGGTCTATT 660CTTTTGATTT ATAAGGGATT TTGCCGATTT CGGCCTATTG GTTAAAAAAT GAGCTGATTT 720AACAAAAATT TAACGCGAAT TTTAACAAAA TATTAACGTT TACAATTTGA TCTGCGCTCG 780GTCGTTCGGC TGCGGCGAGC GGTATCAGCT CACTCAAAGG CGGTAATACG GTTATCCACA 840GAATCAGGGG ATAACGCAGG AAAGAACATG TGAGCAAAAG GCCAGCAAAA GGCCAGGAAC 900CGTAAAAAGG CCGCGTTGCT GGCGTTTTTC CATAGGCTCC GCCCCCCTGA CGAGCATCAC 960AAAAATCGAC GCTCAAGTCA GAGGTGGCGA AACCCGACAG GACTATAAAG ATACCAGGCG 1020TTTCCCCCTG GAAGCTCCCT CGTGCGCTCT CCTGTTCCGA CCCTGCCGCT TACCGGATAC 1080CTGTCCGCCT TTCTCCCTTC GGGAAGCGTG GCGCTTTCTC ATAGCTCACG CTGTAGGTAT 1140CTCAGTTCGG TGTAGGTCGT TCGCTCCAAG CTGGGCTGTG TGCACGAACC CCCCGTTCAG 1200CCCGACCGCT GCGCCTTATC CGGTAACTAT CGTCTTGAGT CCAACCCGGT AAGACACGAC 1260TTATCGCCAC TGGCAGCAGC CACTGGTAAC AGGATTAGCA GAGCGAGGTA TGTAGGCGGT 1320GCTACAGAGT TCTTGAAGTG GTGGCCTAAC TACGGCTACA CTAGAAGGAC AGTATTTGGT 1380ATCTGCGCTC TGCTGAAGCC AGTTACCTTC GGAAAAAGAG TTGGTAGCTC TTGATCCGGC 1440AAACAAACCA CCGCTGGTAG CGGTGGTTTT TTTGTTTGCA AGCAGCAGAT TACGCGCAGA 1500AAAAAAGGAT CTCAAGAAGA TCCTTTGATC TTTTCTACGG GGTCTGACGC TCAGTGGAAC 1560GAAAACTCAC GTTAAGGGAT TTTGGTCATG AGATTATCAA AAAGGATCTT CACCTAGATC 1620CTTTTAAATT AAAAATGAAG TTTTAAATCA ATCTAAAGTA TATATGAGTA AACTTGGTCT 1680GACAGTTACC AATGCTTAAT CAGTGAGGCA CCTATCTCAG CGATCTGTCT ATTTCGTTCA 1740TCCATAGTTG CCTGACTCCC CGTCGTGTAG ATAACTACGA TACGGGAGGG CTTACCATCT 1800GGCCCCAGTG CTGCAATGAT ACCGCGAGAC CCACGCTCAC CGGCTCCAGA TTTATCAGCA 1860ATAAACCAGC CAGCCGGAAG GGCCGAGCGC AGAAGTGGTC CTGCAACTTT ATCCGCCTCC 1920ATCCAGTCTA TTAATTGTTG CCGGGAAGCT AGAGTAAGTA GTTCGCCAGT TAATAGTTTG 1980CGCAACGTTG TTGCCATTGC TGCAGGCATC GTGGTGTCAC GCTCGTCGTT TGGTATGGCT 2040TCATTCAGCT CCGGTTCCCA ACGATCAAGG CGAGTTACAT GATCCCCCAT GTTGTGCAAA 2100AAAGCGGTTA GCTCCTTCGG TCCTCCGATC GTTGTCAGAA GTAAGTTGGC CGCAGTGTTA 2160TCACTCATGG TTATGGCAGC ACTGCATAAT TCTCTTACTG TCATGCCATC CGTAAGATGC 2220TTTTCTGTGA CTGGTGAGTA CTCAACCAAG TCATTCTGAG AATAGTGTAT GCGGCGACCG 2280AGTTGCTCTT GCCCGGCGTC AACACGGGAT AATACCGCGC CACATAGCAG AACTTTAAAA 2340GTGCTCATCA TTGGAAAACG TTCTTCGGGG CGAAAACTCT CAAGGATCTT ACCGCTGTTG 2400AGATCCAGTT CGATGTAACC CACTCGTGCA CCCAACTGAT CTTCAGCATC TTTTACTTTC 2460ACCAGCGTTT CTGGGTGAGC AAAAACAGGA AGGCAAAATG CCGCAAAAAA GGGAATAAGG 2520GCGACACGGA AATGTTGAAT ACTCATACTC TTCCTTTTTC AATATTATTG AAGCAGACAG 2580TTTTATTGTT CATGATGATA TATTTTTATC TTGTGCAATG TAACATCAGA GATTTTGAGA 2640CACAACGTGG CTTTGTTGAA TAAATCGAAC TTTTGCTGAG TTGACTCCCC GCGCGCGATG 2700GGTCGAATTT GCTTTCGAAA AAAAAGCCCG CTCATTAGGC GGGCTAAAAA AAAGCCCGCT 2760CATTAGGCGG GCTCGAATTT CTGCCATTCA TCCGCTTATT ATCACTTATT CAGGCGTAGC 2820AACCAGGCGT TTAAGGGCAC CAATAACTGC CTTAAAAAAA TTACGCCCCG CCCTGCCACT 2880CATCGCAGTA CTGTTGTAAT TCATTAAGCA TTCTGCCGAC ATGGAAGCCA TCACAGACGG 2940CATGATGAAC CTGAATCGCC AGCGGCATCA GCACCTTGTC GCCTTGCGTA TAATATTTGC 3000CCATAGTGAA AACGGGGGCG AAGAAGTTGT CCATATTCGC CACGTTTAAA TCAAAACTGG 3060TGAAACTCAC CCAGGGATTG GCTGAGACGA AAAACATATT CTCAATAAAC CCTTTAGGGA 3120AATAGGCCAG GTTTTCACCG TAACACGCCA CATCTTGCGA ATATATGTGT AGAAACTGCC 3180GGAAATCGTC GTGGTATTCA CTCCAGAGCG ATGAAAACGT TTCAGTTTGC TCATGGAAAA 3240CGGTGTAACA AGGGTGAACA CTATCCCATA TCACCAGCTC ACCGTCTTTC ATTGCCATAC 3300GAAATTCCGG ATGAGCATTC ATCAGGCGGG CAAGAATGTG AATAAAGGCC GGATAAAACT 3360TGTGCTTATT TTTCTTTACG GTCTTTAAAA AGGCCGTAAT ATCCAGCTAA ACGGTCTGGT 3420TATAGGTACA TTGAGCAACT GACTGAAATG CCTCAAAATG TTCTTTACGA TGCCATTGGG 3480ATATATCAAC GGTGGTATAT CCAGTGATTT TTTTCTCCAT TTTAGCTTCC TTAGCTCCTG 3540AAAATCTCGA TAACTCAAAA AATACGCCCG GTAGTGATCT TATTTCATTA TGGTGAAAGT 3600TGGAACCTCT TACGTGCCGA TCAACGTCTC ATTTTCGCCA AAAGTTGGCC CAGGGCTTCC 3660CGGTATCAAC AGGGACACCA GGATTTATTT ATTCTGCGAA GTGATCTTCC GTCACAGGTA 3720TTTATTCGAA GACGAAAGGG CATCGCGCGC GGGGAATTCC CGGGAGAGCT CGATATCGCA 3780TGCGGTACCT CTAGAAGAAG CTTGGAGACA AGGTAAAGGA TAAAACAGCA CAATTCCAAG 3840AAAAACACGA TTTAGAACCT AAAAAGAACG AATTTGAACT AACTCATAAC CGAGAGGTAA 3900AAAAAGAACG AAGTCGAGAT CAGGGAATGA GTTTATAAAA TAAAAAAAGC ACCTGAAAAG 3960GTGTCTTTTT TTGATGGTTT TGAACTTGTT CTTTCTTATC TTGATACATA TAGAAATAAC 4020GTCATTTTTA TTTTAGTTGC TGAAAGGTGC GTTGAAGTGT TGGTATGTAT GTGTTTTAAA 4080GTATTGAAAA CCCTTAAAAT TGGTTGCACA GAAAAACCCC ATCTGTTAAA GTTATAAGTG 4140ACTAAACAAA TAACTAAATA GATGGGGGTT TCTTTTAATA TTATGTGTCC TAATAGTAGC 4200ATTTATTCAG ATGAAAAATC AAGGGTTTTA GTGGACAAGA CAAAAAGTGG AAAAGTGAGA 4260CCATGGAGAG AAAAGAAAAT CGCTAATGTT GATTACTTTG AACTTCTGCA TATTCTTGAA 4320TTTAAAAAGG CTGAAAGAGT AAAAGATTGT GCTGAAATAT TAGAGTATAA ACAAAATCGT 4380GAAACAGGCG AAAGAAAGTT GTATCGAGTG TGGTTTTGTA AATCCAGGCT TTGTCCAATG 4440TGCAACTGGA GGAGAGCAAT GAAACATGGC ATTCAGTCAC AAAAGGTTGT TGCTGAAGTT 4500ATTAAACAAA AGCCAACAGT TCGTTGGTTG TTTCTCACAT TAACAGTTAA AAATGTTTAT 4560GATGGCGAAG AATTAAATAA GAGTTTGTCA GATATGGCTC AAGGATTTCG CCGAATGATG 4620CAATATAAAA AAATTAATAA AAATCTTGTT GGTTTTATGC GTGCAACGGA AGTGACAATA 4680AATAATAAAG ATAATTCTTA TAATCAGCAC ATGCATGTAT TGGTATGTGT GGAACCAACT 4740TATTTTAAGA ATACAGAAAA CTACGTGAAT CAAAAACAAT GGATTCAATT TTGGAAAAAG 4800GCAATGAAAT TAGACTATGA TCCAAATGTA AAAGTTCAAA TGATTCGACC GAAAAATAAA 4860TATAAATCGG ATATACAATC GGCAATTGAC GAAACTGCAA AATATCCTGT AAAGGATACG 4920GATTTTATGA CCGATGATGA AGAAAAGAAT TTGAAACGTT TGTCTGATTT GGAGGAAGGT 4980TTACACCGTA AAAGGTTAAT CTCCTATGGT GGTTTGTTAA AAGAAATACA TAAAAAATTA 5040AACCTTGATG ACACAGAAGA AGGCGATTTG ATTCATACAG ATGATGACGA AAAAGCCGAT 5100GAAGATGGAT TTTCTATTAT TGCAATGTGG AATTGGGAAC GGAAAAATTA TTTTATTAAA 5160GAGTAGTTCA ACAAACGGGC CAGTTTGTTG AAGATTAGAT GCTATAATTG TTATTAAAAG 5220GATTGAAGGA TGCTTAGGAA GACGAGTTAT TAATAGCTGA ATAAGAACGG TGCTCTCCAA 5280ATATTCTTAT TTAGAAAAGC AAATCTAAAA TTATCTGAAA AGGGAATGAG AATAGTGAAT 5340GGACCAATAA TAATGACTAG AGAAGAAAGA ATGAAGATTG TTCATGAAAT TAAGGAACGA 5400ATATTGGATA AATATGGGGA TGATGTTAAG GCTATTGGTG TTTATGGCTC TCTTGGTCGT 5460CAGACTGATG GGCCCTATTC GGATATTGAG ATGATGTGTG TCATGTCAAC AGAGGAAGCA 5520GAGTTCAGCC ATGAATGGAC AACCGGTGAG TGGAAGGTGG AAGTGAATTT TGATAGCGAA 5580GAGATTCTAC TAGATTATGC ATCTCAGGTG GAATCAGATT GGCCGCTTAC ACATGGTCAA 5640TTTTTCTCTA TTTTGCCGAT TTATGATTCA GGTGGATACT TAGAGAAAGT GTATCAAACT 5700GCTAAATCGG TAGAAGCCCA AACGTTCCAC GATGCGATTT GTGCCCTTAT CGTAGAAGAG 5760CTGTTTGAAT ATGCAGGCAA ATGGCGTAAT ATTCGTGTGC AAGGACCGAC AACATTTCTA 5820CCATCCTTGA CTGTACAGGT AGCAATGGCA GGTGCCATGT TGATTGGTCT GCATCATCGC 5880ATCTGTTATA CGACGAGCGC TTCGGTCTTA ACTGAAGCAG TTAAGCAATC AGATCTTCCT 5940TCAGGTTATG ACCATCTGTG CCAGTTCGTA ATGTCTGGTC AACTTTCCGA CTCTGAGAAA 6000CTTCTGGAAT CGCTAGAGAA TTTCTGGAAT GGGATTCAGG AGTGGACAGA ACGACACGGA 6060TATATAGTGG ATGTGTCAAA ACGCATACCA TTTTGAACGA TGACCTCTAA TAATTGTTAA 6120TCATGTTGGT TACGTATTTA TTAACTTCTC CTAGTATTAG TAATTATCAT GGCTGTCATG 6180GCGCATTAAC GGAATAAAGG GTGTGCTTAA ATCGGGCCAT TTTGCGTAAT AAGAAAAAGG 6240ATTAATTATG AGCGAATTGA ATTAATAATA AGGTAATAGA TTTACATTAG AAAATGAAAG 6300GGGATTTTAT GCGTGAGAAT GTTACAGTCT ATCCCGGCAT TGCCAGTCGG GGATATTAAA 6360AAGAGTATAG GTTTTTATTG CGATAAACTA GGTTTCACTT TGGTTCACCA TGAAGATGGA 6420TTCGCAGTTC TAATGTGTAA TGAGGTTCGG ATTCATCTAT GGGAGGCAAG TGATGAAGGC 6480TGGCGCTCTC GTAGTAATGA TTCACCGGTT TGTACAGGTG CGGAGTCGTT TATTGCTGGT 6540ACTGCTAGTT GCCGCATTGA AGTAGAGGGA ATTGATGAAT TATATCAACA TATTAAGCCT 6600TTGGGCATTT TGCACCCCAA TACATCATTA AAAGATCAGT GGTGGGATGA ACGAGACTTT 6660GCAGTAATTG ATCCCGACAA CAATTTGATT AGCTTTTTTC AACAAATAAA AAGCTAAAAT 6720CTATTATTAA TCTGTTCAGC AATCGGGCGC GATTGCTGAA TAAAAGATAC GAGAGACCTC 6780TCTTGTATCT TTTTTATTTT GAGTGGTTTT GTCCGTTACA CTAGAAAACC GAAAGACAAT 6840AAAAATTTTA TTCTTGCTGA GTCTGGCTTT CGGTAAGCTA GACAAAACGG ACAAAATAAA 6900AATTGGCAAG GGTTTAAAGG TGGAGATTTT TTGAGTGATC TTCTCAAAAA ATACTACCTG 6960TCCCTTGCTG ATTTTTAAAC GAGCACGAGA GCAAAACCCC CCTTTGCTGA GGTGGCAGAG 7020GGCAGGTTTT TTTGTTTCTT TTTTCTCGTA AAAAAAAGAA AGGTCTTAAA GGTTTTATGG 7080TTTTGGTCGG CACTGCCGAC AGCCTCGCAG GACACACACT TTATGAATAT AAAGTATAGT 7140GTGTTATACT TTACTTGGAA GTGGTTGCCG GAAAGAGCGA AAATGCCTCA CATTTGTGCC 7200ACCTAAAAAG GAGCGATTTA CATATGAGTT ATGCAGTTTG TAGAATGCAA AAAGTGAAAT 7260CAGGGGGATC CTCTAGAGTC GAGCTCAAGC TAGCTTGGTA CGTACCAGAT CTGAGATCAC 7320GCGTTCTAGA GGTCGA 7336 27 NUCLEIC ACID DOUBLE UNKNOWN SPHI/STUI FRAGMENTIN pGBSCC-4 4 CATATGATCA GTACTAAGAC CCCTAGG 27 31 NUCLEIC ACID DOUBLEUNKNOWN SPHI/STUI FRAGMENT IN pGBSCC-4 5 CCTAGGGGTC TTAGTACTGATCATATGCAT G 31 41 NUCLEIC ACID DOUBLE UNKNOWN SPHI/STUI FRAGMENT INpGBSSC-3, FIGURE 7 6 CTGCAGCAGC GGCGGCAATC AGTACTAAGA CCCCTAGGCC T 41 24NUCLEIC ACID SINGLE LINEAR NDEI RESTRICTION SITE AT THE ATG INITIATIONCODON OF THE LACZ GENE IN PTZ18R 7 CAGGAAACAC ATATGACCAT GATT 24 108NUCLEIC ACID DOUBLE UNKNOWN LACTASE TERMINATOR 8 TCGACGCGGC CGCAGATCTGATATCTCGAG AATTTATACT TAGATAAGTA TGTACTTACA 60 GGTATATTTC TATGAGATACTGATGTATAC ATGCATGATA ATATTTAA 108 44 NUCLEIC ACID DOUBLE UNKNOWNSALI/XHOI FRAGMENT IN pGBSCC-6 9 TCGACAAAAA TGATCAGTAC TAAGACTCCTAGGCCTATCG ATTC 44 44 NUCLEIC ACID DOUBLE UNKNOWN SALI/XHOI FRAGMENT INpGBSCC-6 10 TCGAGAATCG ATAGGCCTAG GAGTCTTAGT ACTGATCATT TTTG 44 158NUCLEIC ACID DOUBLE UNKNOWN SALI/XHOI SYNTHETIC DNA IN PLASMID pGBSCC-1111 TCGACAAAAA TGTTGGCTCG AGGTTTGCCA TTGAGATCCG CTTTGGTTAA GGCTTGTCCA 60CCAATCTTGT CCACTGTTGG TGAAGGTTGG GGTCACCACA GAGTTGGTAC TGGTGAAGGT 120GCTGGTATCA GTACTAAGAC TCCTAGGCCT ATCGATTC 158 158 NUCLEIC ACID DOUBLEUNKNOWN SALI/XHOI SYNTHETIC DNA IN PLASMID pGBSCC-11 12 TCGAGAATCGATAGGCCTAG GAGTCTTAGT ACTGATACCA GCACCTTCAC CAGTACCAAC 60 TCTGTGGTGACCCCAACCTT CACCAACAGT GGACAAGATT GGTGGACAAG CCTTAACCAA 120 AGCGGATCTCAATGGCAAAC CTCGAGCCAA CATTTTTG 158 161 NUCLEIC ACID DOUBLE UNKNOWNSALI/XHOI SYNTHETIC DNA IN pGBSSC-14 13 TCGACAAAAA TGTTGTCTCG AGCTATCTTCAGAAACCCAG TTATCAACAG AACTTTGTTG 60 AGAGCTAGAC CAGGTGCTTA CCACGCTACTAGATTGACTA AGAACACTTT CATCCAATCC 120 AGAAAGTACA TCAGTACTAA GACTCCTAGGCCTATCGATT C 161 161 NUCLEIC ACID DOUBLE UNKNOWN SALI/XHOI SYNTHETIC DNAIN pGBSCC-14 14 TCGAGAATCG ATAGGCCTAG GAGTCTTAGT ACTGATGTAC TTTCTGGATTGGATGAAAGT 60 GTTCTTAGTC AATCTAGTAG CGTGGTAAGC ACCTGCTCTA GCTCTCAACAAAGTTCTGTT 120 GATAACTGGG TTTCTGAAGA TAGCTCGAGA CAACATTTTT G 161 30NUCLEIC ACID DOUBLE LINEAR OLIGOMER 17 ALPHA-1 15 AGTGGCCACT TTGGGACGCCCAGAGAATTC 30 36 NUCLEIC ACID DOUBLE LINEAR OLIGOMER 17 ALPHA-2 16GAGGCTCCTG GGGTACTTGG CACCAGAGTG CTTGGT 36 43 NUCLEIC ACID SINGLE LINEARSEQUENCE OF pGB17 ALPHA-3 MUTATED BY SITE DIRECTED MUTAGENESIS, FIGURE23 17 TCTTTGTCCT GACTGCTGCC ACCCAGACAC AATGTGGCTG CTC 43 43 NUCLEIC ACIDSINGLE LINEAR SYNTHETIC OLIGOMER 17 ALPHA-3 WITH SALI SITE 18 TCTTTGTCCTGACTGCTGCC AGTCGACAAA AATGTGGCTG CTC 43 31 NUCLEIC ACID DOUBLE LINEARSEQUENCE OF pGB17 ALPHA-3 MUTATED BY SITE DIRECTED MUTAGENESIS TO CREATEA NDEI SITE, FIGURE 25 19 GCTGCCACCC AGACACAATG TGGCTGCTCC T 31 31NUCLEIC ACID DOUBLE LINEAR SYNTHETIC OLIGOMER 17 ALPHA-4 20 GCTGCCACCCAGACCATATG TGGCTGCTCC T 31 30 NUCLEIC ACID SINGLE LINEAR OLIGOMER C21-121 GATGATGCTG CAGGTAAGCA GAGAGAATTC 30 15 NUCLEIC ACID SINGLE LINEAROLIGOMER C21-2 22 AAGCAGAGAG AATTC 15 36 NUCLEIC ACID SINGLE LINEAROLIGOMER C21-3 23 CTTCCACCGG CCCGATAGCA GGTGAGCGCC ACTGAG 36 36 NUCLEICACID SINGLE LINEAR OLIGOMER C21-4 24 CTCACTGATA TCCATATGGT CCTCGCAGGGCTGCTG 36 27 NUCLEIC ACID SINGLE LINEAR OLIGOMER C21-5 25 AGCTCAGAATTCCTTCTGGA TGGTCAC 27 12 NUCLEIC ACID DOUBLE UNKNOWN FIGURE 29, pGBC21-226 CCAGCCATGG TC 12 9 NUCLEIC ACID DOUBLE UNKNOWN FIGURE 29, pGBC21-2 27AAGGAATTC 9 21 NUCLEIC ACID SINGLE LINEAR OLIGOMER C21-4 28 CTCACTGATATCCATATGGT C 21 15 NUCLEIC ACID SINGLE LINEAR OLIGOMER C21-5 29AAGGAATTCT GAGCT 15 36 NUCLEIC ACID SINGLE LINEAR OLIGOMER C21-6 30CCTCTGCCTG GGTCGACAAA AATGGTCCTC GCAGGG 36 36 NUCLEIC ACID DOUBLEUNKNOWN PGBC21-2, FIGURE 33 31 CCTCTGCCTG GGTCTCCAGC CATGGTCCTC GCAGGG36 18 NUCLEIC ACID SINGLE LINEAR OLIGOMER 11 BETA-1 32 GGCAGTGTGCTGACACGA 18 30 NUCLEIC ACID SINGLE LINEAR OLIGOMER 11 BETA-2 33CCGCACCCTG GCCTTTGCCC ACAGTGCCAT 30 36 NUCLEIC ACID SINGLE LINEAROLIGOMER 11 BETA-3 34 CAGCTCAAAG AGAGTCATCA GCAAGGGGAA GGCTGT 36 42NUCLEIC ACID SINGLE LINEAR OLIGOMER 11 BETA-4 35 TTTGATATCG AATTCCATATGGGCACCAGA GGTGCTGCAG CC 42 42 NUCLEIC ACID SINGLE LINEAR OLIGOMER 11BETA-5 36 TAACGATATC CTCGAGGGTA CCTACTGGAT GGCCCGGAAG GT 42 39 NUCLEICACID SINGLE LINEAR OLIGOMER 11 BETA-6 37 CTTCAGTCGA CAAAAATGGGCACCAGAGGT GCTGCAGCC 39 18 NUCLEIC ACID DOUBLE UNKNOWN REGION IN 11 BETAcDNA HOMOLOGOUS TO PRIMERS, FIGURE 36 38 CGCCTACTGG GCACCAGA 18 21NUCLEIC ACID DOUBLE UNKNOWN REGION IN 11 BETA cDNA HOMOLOGOUS TOPRIMERS, FIGURE 36 39 GCCATCCAGT AGTCGTGTCA G 21 30 NUCLEIC ACID SINGLELINEAR OLIGOMER 11 BETA-4, FIGURE 36 40 TTTGATATCG AATTCCATAT GGGCACCAGA30 33 NUCLEIC ACID SINGLE LINEAR OLIGOMER 11 BETA-5, FIGURE 36 41GCCATCCAGT AGGTACCCTC GAGGATATCG TTA 33 27 NUCLEIC ACID SINGLE UNKNOWNOLIGOMER 11 BETA-6, FIGURE 37 42 CTTCAGTCGA CAAAAATGGG CACCAGA 27 39NUCLEIC ACID SINGLE LINEAR OLIGOMER ADX-1 43 CTTCAGTCGA CAAAAATGAGCAGCTCAGAA GATAAAATA 39 40 NUCLEIC ACID SINGLE LINEAR OLIGOMER ADX-2 44TGTAAGGTAC CCGGGATCCT TATTCTATCT TTGAGGAGTT 40 18 NUCLEIC ACID DOUBLEUNKNOWN REGION OF ADX mRNA/cDNA HOMOLOGOUS TO THE PRIMERS, FIGURE 38 45CGAGCGCAGA GCAGCTCA 18 18 NUCLEIC ACID DOUBLE UNKNOWN REGION OF ADXmRNA/cDNA HOMOLOGOUS TO THE PRIMERS, FIGURE 38 46 ATAGAATAAA TAGGAATA 1827 NUCLEIC ACID SINGLE LINEAR OLIGOMER ADX-1, FIGURE 38 47 CTTCAGTCGACAAAAATGAG CAGCTCA 27 28 NUCLEIC ACID SINGLE LINEAR OLIGOMER ADX-2,FIGURE 38 48 ATAGAATAAG GATCCCGGGT ACCTTACA 28 15 NUCLEIC ACID SINGLELINEAR OLIGOMER ADR-1 49 GGCTGGGATC TAGGC 15 36 NUCLEIC ACID SINGLELINEAR OLIGOMER ADR-2 50 CACCACACAG ATCTGGGGGG TCTGCTCCTG TGGGGA 36 36NUCLEIC ACID SINGLE LINEAR OLIGOMER ADR-3 51 TTCCATCAGC CGCTTCCTCGGGCGAGCGGC CTCCCT 36 36 NUCLEIC ACID SINGLE LINEAR OLIGOMER ADR-4 52CGAGTGTCGA CAAAAATGTC CACACAGGAG CAGACC 36 36 NUCLEIC ACID SINGLE LINEAROLIGOMER ADR-5 53 CGTGCTCGAG GTACCTCAGT GCCCCAGCAG CCGCAG 36 50 NUCLEICACID SINGLE LINEAR SYNTHETIC OLIGOMER USED TO SCREEN BOVINE ADRENALCORTEX cDNA LIBRARY 54 TGCCAGTTCG TAGAGCACAT TGGTGCGTGG CGGGTTAGTGATGTCCAGGT 50 18 NUCLEIC ACID DOUBLE UNKNOWN REGION OF ADR cDNAHOMOLOGOUS TO PRIMERS, FIGURE 40 55 CAGCACTTCT CCACACAG 18 18 NUCLEICACID DOUBLE UNKNOWN REGION OF ADR cDNA HOMOLOGOUS TO PRIMERS, FIGURE 4056 GGGCACTGAG CCTAGATC 18 27 NUCLEIC ACID SINGLE LINEAR PRIMER ADR4,FIGURE 40 57 CGAGTGTCGA CAAAAATGTC CACACAG 27 24 NUCLEIC ACID SINGLELINEAR PRIMER ADR5, FIGURE 40 58 GGGCACTGAG GTACCTCGAG CACG 24 25NUCLEIC ACID SINGLE LINEAR 59 GCGCTCAGCG GCCGCTTTCC AGTCG 25 21 NUCLEICACID SINGLE LINEAR 60 AATTGCGGCC GCGTACGTAT G 21 21 NUCLEIC ACID SINGLELINEAR 61 AATTCATACG TACGCGGCCG C 21 55 NUCLEIC ACID SINGLE LINEAR 62GAATTCATAC GTACGCGGCC GCAATTGCGG CCGGTACGTA TAATTCACTG GCCGT 55 14NUCLEIC ACID SINGLE LINEAR 63 CAACGCGTCC TAGG 14 22 NUCLEIC ACID SINGLELINEAR 64 AATTCCTAGG ACGCGTTGAG CT 22 33 NUCLEIC ACID SINGLE LINEAR 65GATCCGCAGA TATCATCTAG ATCCCGGGTA GAT 33 39 NUCLEIC ACID SINGLE LINEAR 66AGAGCTCAAG ATCTACCCGG GATCTAGATG ATATCTGCG 39 34 NUCLEIC ACID SINGLELINEAR 67 CTTGAGCTCT ACGCAGCTGG TCGACACCTA GGAG 34 28 NUCLEIC ACIDSINGLE LINEAR 68 AATTCTCCTA GGTGTCGACC AGCTGCGT 28 40 NUCLEIC ACIDSINGLE LINEAR 69 GCGGATCTGC TCGAAGATTG CCTGCGCGTT GGGCTTGATC 40 15NUCLEIC ACID SINGLE LINEAR 70 TCGACGGACG CGTGG 15 14 NUCLEIC ACID SINGLELINEAR 71 TCGACCACGC GTCC 14 35 NUCLEIC ACID SINGLE LINEAR 72 TGGCCGTCGTTTTACTCCTG CGCCTGATGC GGTAT 35 15 NUCLEIC ACID SINGLE LINEAR 73GGCCGCAAAA CCAAA 15 15 NUCLEIC ACID SINGLE LINEAR 74 AGCTTTTGGT TTTGC 1520 NUCLEIC ACID SINGLE LINEAR 75 GATCTATCGA TGCGGCCGCG 20 20 NUCLEICACID SINGLE LINEAR 76 CGCGCGCGGC CGCATCGATA 20 14 NUCLEIC ACID SINGLELINEAR 77 AATTGGACGC GTCC 14 12 NUCLEIC ACID SINGLE LINEAR 78 CACAAGCTTGTG 12 12 NUCLEIC ACID SINGLE LINEAR 79 TCGAGGGAAG CT 12

What we claim is:
 1. A process for the selective oxidation of ahydrocortisone precursor compound to an oxidized product which processcomprises the steps of: (a) incubating the compound to be oxidized inthe presence of a recombinant host cell or progeny thereof comprising atleast one expression cassette comprising a heterologous DNA encoding twoor more human or bovine enzymes from the metabolic pathway for thebioconversion of cholesterol to hydrocortisone wherein one of theenzymes catalyzes the oxidation of 17α-hydroxyprogesterone tocortexolone and the remaining one or more enzymes catalyze at least onereaction selected from the group consisting of: the oxidation ofcholesterol to pregnenolone; the oxidation of pregnenolone toprogesterone; the oxidation of progesterone to 17α-hydroxyprogesterone;and the oxidation of cortexolone to hydrocortisone; wherein theheterologous DNA is operably linked to control sequences required toexpress the encoded enzymes in a recombinant host wherein the host is aspecies of Saccharomyces, Kluyveromyces or Escherichia coli and whereinthe incubation is performed under conditions where the compound isoxidized and oxidized product accumulates, and (b) recovering theoxidized product.
 2. The process according to claim 1, wherein oneoxidation is of 17α-hydroxyprogesterone to cortexolone and the otheroxidation is selected from the group consisting of: the oxidation ofcholesterol to pregnenolone; the oxidation of pregnenolone toprogesterone; the oxidation of cortexolone to hydrocortisone.
 3. Theprocess according to claim 1 wherein the expression cassette(s) compriseheterologous DNA encoding two human or bovine enzymes from the metabolicpathway for the bioconversion of cholesterol to hydrocortisone.
 4. Aprocess for the selective oxidation of a hydrocortisone precursorcompound to an oxidized product, which process comprises the steps of:(a) incubating the compound to be oxidized in the presence of arecombinant host cell or progeny thereof comprising a heterologous DNAencoding two or more human or bovine enzymes from the metabolic pathwayfor the bioconversion of cholesterol to hydrocortisone wherein one ofthe enzymes catalyzes the oxidation of 17α-hydroxyprogesterone tocortexolone and the remaining one or more enzymes catalyzes at least onereaction selected from the group consisting of: the oxidation ofcholesterol to pregnenolone; the oxidation of pregnenolone toprogesterone; the oxidation of progesterone to 17α-hydroxyprogesterone;and the oxidation of cortexolone to hydrocortisone; wherein theheterologous DNA is operably linked to control sequences required toexpress the encoded enzymes in the recombinant host wherein the host isa species of Saccharomyces, Kluyveromyces or Escherichia coli andwherein the incubation is performed under conditions where the compoundis oxidized and the oxidized product accumulates, and (b) recovering theoxidized product.
 5. The process according to claim 4 wherein the enzymethat catalyzes the oxidation of 17α-hydroxyprogesterone to cortexoloneis steroid-21-hydroxylase (P₄₅₀C21) and the remaining one or moreenzymes includes at least one steroid-17-α-hydroxylase ((P₄₅₀17α).